1. As you already know, the force with which a body, due to its attraction to the Earth, acts on a support or suspension is called body weight P.
Body weight is applied to the support or suspension; in contrast, gravity is applied to the body. Weight and gravity are not only different points of application, but also of different nature: gravity is gravitational force, and weight is elastic force.
From the 7th grade physics course, you also know that if a body suspended by threads or placed on a support is at rest or moves uniformly and rectilinearly, then its weight is equal in modulus to the force of gravity:
P = mg.
2. Let us now assume that the body, together with the support or suspension, is moving relative to the Earth with acceleration. In this case, will body weight and gravity be equal?
Consider the movement of a person in an elevator. Let the lift have acceleration a downward (fig. 52). In the inertial frame of reference connected with the Earth, a person is influenced by the force of gravity directed downward and the force of elasticity from the side of the floor of the elevator directed upward. The elastic force in this case is called support reaction force and denoted by the letter N... The resultant of these forces imparts acceleration to the person.
Using Newton's second law, you can write in vector form:
F = ma,
F heavy + N = ma.
Let's direct the axis Y vertically downward and write this equation in projections onto this axis, taking into account that F heavy = mg, the projection of acceleration and gravity on the axis Y are positive, and the projection of the reaction force of the support is negative. We get:
mg – N = ma.
Hence:
N = mg – ma = m(g – a).
According to Newton's third law, the modulus of the weight of a body is equal to the reaction force of the support:
P = N.
Then
P = m(g – a).
It can be seen from the resulting formula that the weight of the body is less than the force of gravity. In this way, if the body together with the support or suspension moves downward with an acceleration that is directed in the same way as the acceleration of gravity, then its weight is less than the force of gravity, that is, less than the weight of the body at rest.
You experience a decrease in weight while in an elevator at the moment it starts moving down.
If the acceleration of the body is equal to the acceleration of gravity a = g then body weight P= 0. This state is called the state weightlessness... In a state of weightlessness, astronauts are in a spacecraft during flight, since they move around the Earth with a centripetal acceleration equal to the acceleration of free fall.
But not only astronauts experience a state of weightlessness. A runner can be in this state for short periods of time when both feet are off the ground; ski jumper during the flight.
3. Consider again the movement of the elevator and the person standing in it. But only now the elevator has acceleration a pointing up (fig. 53).
Using Newton's second law, you can write:
F = ma,
F heavy + N= ma.
Aligning the axis Y vertically downward, we write this equation in projections onto this axis:
mg – N = –ma; N = mg + ma; N = m(g + a).
Insofar as P = N, then
P = m(g + a).
It can be seen from the formula that the weight in this case is greater than the force of gravity. In this way, if the body, together with the support or suspension, moves with an acceleration directed opposite to the acceleration of free fall, then its weight is greater than the force of gravity, i.e., greater than the weight of the body at rest.
The increase in body weight caused by accelerating movement is called overload.
You experience an overload in the elevator when it starts moving up. Cosmonauts and jet pilots experience enormous overloads during takeoff and landing; pilots performing a "loophole" aerobatics at its lowest point. In order to reduce the pressure on the skeleton of the astronauts during takeoff, special chairs have been made in which the astronauts are in a reclining position. In this case, the force of pressure that acts on the astronaut is distributed over a large area, and the pressure on the skeleton becomes less than in the case when the astronaut is in a sitting position.
4. An example of solving the problem
What is the weight of a 70 kg pilot performing a "loop" at the lower and upper points of the trajectory, if the loop radius is 200 m, and the aircraft speed when passing the loop is 100 m / s?
|
Given: |
Solution |
|
m= 70 kg R= 200 m v= 100 m / s g= 10 m / s 2 |
The pilot is affected by gravity at the lower and upper points of the trajectory. F heavy weight and reaction force from the chair N(fig. 54). The reaction force of the support is equal in magnitude to the pilot's weight: P = N. In accordance with Newton's second law, you can write: N + F heavy = ma. |
|
P 1? P 2? |
For the bottom point of the trajectory, this is the equation in projections onto the axis Y(fig. 54, a) will look like:
–N 1 + F heavy = - ma, or N 1 – mg= ma.
Hence,
P 1 = N 1 = ma+ mg= m(a + g).
For the top point of the trajectory (Fig. 54, b) can be written:
N 1 + F heavy = ma.
From here
N 1 = ma – mg.
Hence,
P 2 = N 1 = m(a – g).
Insofar as a=, then
P 1 = m + g; P 2 =– g.
P 1 = 70 kg + 10 m / s 2 = 4200 N;
P 2 = 70 kg - 10 m / s 2 = 2800 N.
If the force of gravity acting on the pilot F heavy = 70 kg 10 m / s 2 = 700 N, then its weight at the lowest point of the trajectory is 6 times greater than the force of gravity: == 6. They say that the pilot experiences a six-fold overload.
At the top of the trajectory, the pilot experiences a four-fold overload: == 4.
Answer: P 1 = 4200 N; P 2 = 2800 N.
Self-test questions
1. What is called body weight? What is the nature of body weight?
2. In what case is the modulus of the body weight equal to the gravity?
3. How does the weight of the body change when it moves with acceleration directed upwards; down?
4. What state is called the state of weightlessness? When does it start?
5. Which condition is called overload? When are overloads experienced?
Task 15
1. The lift starts moving downward with an acceleration of 2 m / s 2. What is the weight of a 60 kg person standing in this elevator?
2. With what force does a car weighing 1 tonne press on the middle of a convex bridge with a radius of curvature of 30 m? Vehicle speed is 72 km / h.
3. A stone weighing 400 g is rotated uniformly in a vertical plane on a rope 1 m long at a speed of 2 m / s (Fig. 55). What is the tensile force of the rope when the stone passes the upper and lower points of the trajectory?
Task number 6
Question:
Two forces are applied to the body, the moduli of which are 10 N and 20 N. It is known that the forces are directed along one straight line and in opposite directions. What will be the resultant force (in N)?
Write down the number:
________10 ________________
Task number 7
Question:
A body weighing 100 kg is acted upon by a resultant force equal to 20 N. What is the body's acceleration modulus (in m / s 2)?
Write down the number:
_________0,2 _______________
Task number 8
Question:
A body weighing 5 kg rests on the horizontal surface of the table. Determine with what force (in H) the table will act on this body?
Write down the number:
__________49 _______________
Task number 9
Question:
The figure shows two forces acting on the body. Find the modulus of strength F 2(in H), if the body moves to the right with a constant speed of 2 m / s.
Image:
Write down the number:
________17,3 ________________
Task number 10
Question:
A body of mass m moves with an acceleration of 3 m / s 2. How many times should the resultant force increase for the body to start moving with an acceleration of 9 m / s 2?
Write down the number:
______3_________________
The law of universal gravitation. Space speeds
Task number 1
Question:
The proportionality coefficient in the formula describing the law of universal gravitation is numerically equal to ...
1) About 10 9
2) About 10 5
3) About 10 -19
4) About 10 -11
Task number 2
Question:
Choose the values on which the first two cosmic velocities of this planet depend
Choose a few of the 5 answer options:
Weight
2) Albedo
Radius
4) The period of revolution around its axis
5) The period of revolution around its star
Task number 3
Question:
Choose the correct statements
__ Gravitational interaction between bodies always manifests itself in the form of mutual attraction
__ The force of gravity is proportional to the masses of bodies
The force of gravity is inversely proportional to the distance between bodies
The law of universal gravitation is universal and can be applied with high accuracy to any pair of bodies.
Task number 4
Question:
The speed with which a body must move in order to leave the orbit of a given celestial body is ...
Choose one of 4 answer options:
1) The first cosmic speed of a given body
2) The second cosmic speed of a given body
The third cosmic speed of a given body
4) The fourth cosmic speed of a given body
Task number 5
Question:
The pencil rests on the table. What kind of interaction is due to this?
Choose one of 4 answer options:
Gravitational
2) Electromagnetic
3) Strong
Task number 6
Question:
Find the force (in mN) with which two asteroids in open space weighing 10,000 tons each are attracted if the distance between them is 1 km.
Write down the number:
_______6,67 _________________
Task number 7
Question:
In order to make an aircraft an artificial satellite of a planet, this aircraft, departing from this planet, needs to develop a speed of 2 km / s. If the mass of a given planet is 10 23 kg, then what is its radius (in km)?
Write down the number:
______1667,5 _________________
Task number 8
Question:
Find the second cosmic velocity of the Moon in km / s. The Moon's mass is 7.3x10 22 kg, and its radius is 1737 km.
Write down the number:
______1,67 _________________
Task number 9
Question:
Find the force (in TH) with which the Sun acts on Pluto. The mass of the Sun is 2x10 30 kg, the mass of Pluto is 1.3x10 22 kg. The average distance between the Sun and Pluto is taken equal to 5913 million km.
Write down the number:
_____49600 _________________
Task number 10
Question:
Find the radius of the planet (in km), the first space velocity of which is 12 km / s, and the acceleration of gravity is 15 m / s 2.
Write down the number:9600
Gravity. Weight, weightlessness, overload
Task number 1
Question:
Choose the correct statements
Indicate whether the answer options are true or false:
YES) The force of gravity acting on a body is equal to the product of the body's mass and the acceleration of gravity
NO) Body weight is equal to the product of body weight and acceleration due to gravity
NO) Weight is a scalar
YES) Weight is the force acting on a support or suspension
Task number 2
Question:
A person experiences an overload while in an elevator if ...
Choose one of 4 answer options:
1) The elevator is at rest
The elevator goes up
3) The elevator goes down
4) If the person is in his arms
Task number 3
Question:
Astronauts in near-earth orbit experience a state of weightlessness, because ...
1) They are far enough from the Earth so that the force of gravity ceases to act on them
They are in free fall, falling around the Earth.
3) They begin to be attracted by other celestial bodies, and the total action of these bodies balances the force of gravity acting from the Earth
Task number 4
Question:
Match the situation with the effect of this situation
Match all 4 answer options:
The pilot is overloaded
2) The force of gravity acting on the pilot is not equal to his weight
3) The force of gravity acting on the pilot is equal to his weight
4) The pilot experiences weightlessness
4) The plane goes into a tailspin
The plane comes out of the dive
3) The plane flies with horizontal acceleration
2) The plane flies with vertical acceleration
Task number 5
Question:
Is the Earth in a weightless state?
Choose one of 3 answer options:
3) Depending on the choice of reference system
Task number 6
Question:
The waiter raises the tray vertically upward with an acceleration of 3 m / s 2. The weight of the dishes on the tray is 2 kg. Determine the force (in N) with which the dishes act on the tray.
Write down the number:
____________26 _______________
Task number 7
Question:
A bar weighing 400 g is resting on the board. The board is lifted together with the bar and released. Find the force (in N) with which the bar will act on the board during flight.
Write down the number:
_______0 ________________
Task number 8
Question:
A person weighing 50 kg is swinging on a swing, which is attached with two identical ropes. The length of each of the ropes is 2 m. The weight of a person at the moment when he passes the lower point of his trajectory is 1.2 kN. Find the maximum linear velocity (in m / s) at which the person is swinging.
Write down the number:
_______5,29 ___________________
Task number 9
Question:
The car drives over the bridge. At the same time, its weight decreases. Then this bridge ...
Choose one of 4 answer options:
2) Curved down
Bent up
4) Not enough information to draw any conclusions
Task number 10
Question:
The lift moves upward at a speed of 1 m / s. The lift contains a load of 100 kg. With what force (in N) does this load act on the elevator during such a movement?
Write down the number: 981
On the section DE, the car was moving uniformly accelerated, the acceleration vector is directed opposite to the speed vector
On section AB, the car was moving evenly
The acceleration module in section AB is smaller than the acceleration module in section DE.
Three bodies of the same mass, 3 kg each, performed movements. The displacement projection equations are presented in the table. Which graph shows the dependence of the projection of the force on time, acting on each body?
Solve the problems.
9. Suspended to the rope, a body weighing 10 kg rises vertically. With what acceleration does the body move if the cable with a stiffness of 59kN / m lengthened by 2 mm? What is the elastic force in the rope?
Given: SI: Solution:
10. The average height of the satellite above the Earth's surface is 1700 km. Determine the speed of its movement.
Given: SI: Solution:
Solve the problem.
A trolley weighing 5 kg moves under the action of a weight of 2 kg. Determine the thread tension if the coefficient of friction is 0.1.
Given: Solution:
OPTION 2
1. Listed below are the motion of bodies relative to the Earth. What frame of reference associated with one of these bodies cannot be considered inertial? The frame of reference associated with the Earth is considered inertial.
1) the girl runs at a constant speed
2) the car moves evenly along the horizontal part of the road
3) the train is moving uniformly
4) 
hockey puck glides evenly on smooth ice
2. Four forces act on a body weighing 2 kg. What is the acceleration of the body if
F 1 = 20 N, F 2 = 18 N, F 3 = 20 N, F 4 = 16 N.
1) 2 m / s 2 2) 4 m / s 2 3) 1 m / s 2 4) 8 m / s 2
3. What expression determines the value of the first space velocity of the satellite, if the radius of its circular orbit is R, and the acceleration of gravity at this altitude is g?
4. In order for the body in the elevator to experience overload (weight gain), it is necessary:
1) accelerated movement of the elevator up 2) decelerated movement of the elevator up 3) accelerated movement of the elevator down 4) such a state is impossible
5. A man was carrying two identical children on a sled along a horizontal road. Then one child got up from the sled, but the man continued to move at the same constant speed. How did the friction force change in this case?
1) did not change 2) increased 2 times 3) decreased 2 times 4) increased by 50%
6. Along the inclined plane, the bar moves evenly upward. Which vector shown in the figure is redundant or incorrect?
7. The module of speed of a car with a mass of 1000 kg changes in accordance with the graph shown in the figure. Which statement is correct?
2) on the CD section, the car was moving uniformly, the acceleration vector coincides in direction with the speed vector
3) on the section DE, the car was moving uniformly, the acceleration vector coincides in direction with the speed vector
4) the acceleration modulus in the AB section is less than the acceleration modulus in the DE section
 |
7. Using the condition of the problem, establish the correspondence of the equations from the left column of the table with their graphs in the right column.
Three bodies of the same mass, 2 kg each, performed movements. The displacement projection equations are presented in the table. Which graph shows the dependence of the projection of the force on time, acting on each body?
Solve the problems.
8. A bus weighing 15 tons starts to move with an acceleration of 0.7 m / s 2. What is the frictional force on the bus if the engine thrust is 15 kN? Express the answer in kN. What is the coefficient of friction?
Given: SI: Solution:
9. The average height of the satellite above the Earth's surface is 900 km. Determine the speed of its movement.
Given: SI: Solution:
Solve the problem.
10. Two weights of 200 g and 300 g are tied with a thread. Determine the acceleration of the weights and the tension force of the thread between them, if a force of 10 N is applied to a body of mass m 1, directed horizontally to the right.
Given: SI: Solution:
Assessment _____ signature of the teacher ________________ / L.S. Tishkina /
OPTION 3
PART A Choose one correct answer.
1. The parachutist descends vertically at a constant speed of 2 m / s. The frame of reference associated with the Earth is considered inertial. In this case:
1) no forces act on the parachute
2) the force of gravity is balanced by the force of Archimedes acting on the parachute
3) the sum of all forces acting on the parachute is zero
4) the sum of all forces is constant and not equal to zero
2. A body weighing 2 kg is acted upon by forces of 3 N and 4 N directed perpendicular to each other. What is the acceleration of the body?
1) 3.5 m / s 2 2) 2.5 m / s 2 3) 7 m / s 2 4) 10 m / s 2
3. A satellite of mass m moves around the planet in a circular orbit of radius R. Mass of the planet M. What expression determines the value of the acceleration of the satellite's motion?
4. The lift is equipped with spring scales on which a person stands. How will the scale readings change when the elevator moves up and down quickly?
1) up - increase, down - decrease
2) up - decrease, down - increase
3) up - will increase, down - will not change
4) up - will not change, down - will increase
5. A man was carrying a child on a sled along a horizontal road. Then a second child of the same type sat down on the sled, but the person continued to move at the same constant speed. How did the coefficient of friction change in this case?
1) did not change 2) increased 2 times 3) decreased 2 times 4) increased by 50%
6. Along the inclined plane, the bar moves upward at uniform acceleration. Which vector shown in the figure is redundant or incorrect?
7. The module of speed of a car weighing 1000 kg changes in accordance with the graph shown in the figure. Which statement is correct?
1) on the aircraft section, the car was moving uniformly
2) on the CD section, the car was moving uniformly, the acceleration vector is directed opposite to the speed vector.
3) the car was at rest on the EF section
4) the acceleration modulus in the AB section is less than the acceleration modulus in the DE section
 |
8. Using the condition of the problem, establish the correspondence of the equations from the left column of the table with their graphs in the right column.
Three bodies of the same mass, 4 kg each, performed movements. The displacement projection equations are presented in the table. Which graph shows the dependence of the projection of the force on time, acting on each body?
Solve the problems.
9. The lift descends with an acceleration of 2 m / s 2. In the elevator, a load weighing 0.7 kg hangs on a spring with a stiffness of 560 N / m. What is the spring force? How many centimeters is the spring extended?
Given: Solution:
10. The average height of a satellite above the Earth's surface is 600 km. Determine the speed of its movement.
Given: SI: Solution:
Solve the problem.
11. A bar weighing 400 g comes into motion with an acceleration of 0.4 m / s 2 under the action of a load weighing 100 g. Find the friction force and the coefficient of friction of the bar against the surface.
Given: SI: Solution:
Assessment _____ signature of the teacher ________________ / L.S. Tishkina /
OPTION 4
PART A Choose one correct answer
1) the lift falls freely 2) the lift rises evenly
3) the lift moves up slowly 4) the lift moves downward
2. 
Four forces act on a body weighing 2 kg. What is the acceleration of the body if F 1 = 12 N, F 2 = 18 N, F 3 = 20 N, F 4 = 18 N.
1) 6 m / s 2 2) 16 m / s 2 3) 2 m / s 2 4) 4 m / s 2
3. The mass of the Moon is about 81 times less than the mass of the Earth. What is the ratio of the force of universal gravitation F 1, acting from the Earth on the Moon, to the force F 2, acting on the Earth from the Moon?
1) 1/81 2) 81 3) 9 4) 1
4. How to force a 10N weight to stretch the dynamometer spring with a force greater than 10N?
1) move the dynamometer with the kettle down with some acceleration
2) move the dynamometer with a kettlebell upward with some acceleration
3) the dynamometer with a weight should fall freely
4) this is impossible
5. A man was carrying two identical children on a sled along a horizontal road. Then one child got up from the sled, but the man continued to move at the same constant speed. How has changed
coefficient of friction in this case?
1) increased 2 times 2) decreased 2 times 3) increased by 50% 4) did not change
6. On the inclined plane, the block lies motionless. Which vector shown in the figure is redundant or incorrect?
1) 2) 3) 4)
7. The module of speed of a car weighing 1000 kg changes in accordance with the graph shown in the figure. Which statement is correct?
1) 
on the CD section, the car was moving uniformly, the acceleration vector coincides in direction with the speed vector
2) the acceleration module in the AD section is greater than the acceleration module in the DE section
3) on the section DE, the car was moving uniformly, the acceleration vector is directed opposite to the speed vector
4) on section AB, the car moved evenly
8. Using the condition of the problem, establish the correspondence of the equations from the left column of the table with their graphs in the right column.
Three bodies of the same mass, 2 kg each, performed movements. The displacement projection equations are presented in the table. Which graph shows the dependence of the projection of the force on time, acting on each body?
Solve the problems.
9. A car with a mass of 1 t moves with an acceleration of 0.8 m / s 2. A frictional force of 2 kN acts on the vehicle. Determine the engine thrust (answer in kN) and the coefficient of friction.
Given: SI: Solution:
10. The average height of a satellite above the Earth's surface is 300 km. Determine the speed of its movement.
Given: SI: Solution:
Solve the problem.
11. Two weights weighing 200 g and 300 g are suspended on a cord thrown over a fixed block. With what acceleration do the weights move? What is the thread tension?
Given: SI: Solution:
Assessment _____ signature of the teacher ________________ / L.S. Tishkina /
Date "___" _________ 20 ____
Related assignment 12
"Application of the law of conservation of momentum of a body"
Solve tasks:
1. Find the impulse of a truck weighing 10 tons, moving at a speed of 36 km / h, and a passenger car weighing 1 ton, moving at a speed of 25 m / s.
Given: SI: Solution:
2. A train weighing 2000 tons, moving in a straight line, increased the speed from 36 to 72 km / h. Find the change in momentum.
Given: SI: Decision: Given: SI: Decision:
Given: SI: Solution:
Assessment _____ signature of the teacher ________________ / L.S. Tishkina /
Date "___" _________ 20 ____
Related task 15
“Formation and propagation of waves.
Option 1.
The plane flies in a straight line at a constant speed at an altitude of 9 km. The frame of reference associated with the Earth is considered inertial. In this case:
1) no forces act on the plane
2) the plane is not affected by gravity
3) the sum of all forces acting on the plane is zero
4) the force of gravity is equal to the force of Archimedes acting on the plane
A body weighing 1 kg is acted upon by forces of 6 N and 8N, directed perpendicular to each other. What is the acceleration of the body?
1) 2 m / s 2 2) 5 m / s 2 3) 10 m / s 2 4) 14 m / s 2
Satellite massT R
1) 2) 3) 4)
A load weighing 2 kg was suspended to a spring 10 cm long, the stiffness coefficient of which was 500 N / m. What is the length of the spring?
1) 12 cm 2) 13 cm 3) 14 cm 4) 15 cm
A man was carrying a child on a sled along a horizontal road. Then a second child of the same type sat down on the sled, but the man continued at the same constant speed. How did the friction force change in this case?
A bar slides down an inclined plane. Which vector shown in the figure is redundant or incorrect?
1) 2) 3) 4)
2) on the siteDE
3) on the AB section, the car moved evenly
DE
Part B
Three bodies of the same mass, 3 kg each, performed movements. The displacement projection equations are presented in the table. Which graph shows the dependence of the projection of the force on time, acting on each body?
Solve the problems.A body weighing 10 kg suspended from the cable rises vertically. With what acceleration does the body move if the cable with a stiffness of 59 kN / m lengthened by 2 mm? What is the elastic force in the rope?
The average height of the satellite above the Earth's surface is 1700 km. Determine the speed of its movement.
Option2 .
Part A Choose one correct answer.
Listed below are the movements of bodies relative to the Earth. What frame of reference associated with one of these bodies cannot be considered inertial? The frame of reference associated with the Earth is considered inertial.
1) the girl runs at a constant speed
2) the car moves evenly along the horizontal part of the road
3) the train is moving uniformly
4) the hockey puck glides evenly on smooth ice
1) 2 m / s 2 2) 4 m / s 2 3) 1 m / s 2 4) 8 m / s 2
What expression determines the value of the first cosmic speed of the satellite, if the radius of the circular orbitR, and the acceleration of gravity at this heightg?
1) 2) 3) 4)
In order for the body in the elevator to experience overload (weight gain), it is necessary:
1) accelerated movement of the elevator up
2) slow motion of the elevator up
3) accelerated movement of the elevator down
4) such a state is impossible
A man was carrying two identical children on a sled along a horizontal road. Then one child got up from the sled, but the man continued to move at the same constant speed. How did the friction force change in this case?
1) did not change 2) increased 2 times
3) decreased by 2 times 4) increased by 50%
1) 2) 3) 4)
The vehicle speed module with a mass of 1000 kg changes in accordance with the graph shown in the figure. Which statement is correct?
1) on the aircraft section, the car was moving uniformly
2) in section CD
3) on the siteDEthe car was moving uniformly, the acceleration vector coincides in direction with the speed vector.
4) the module of acceleration in the AB section is less than the module of acceleration in the sectionDE
Part B
Using the condition of the problem, match the equations from the left column with their graphs in the right column.
A bus weighing 15 tons starts to move with an acceleration of 0.7 m / s 2 ... What is the frictional force on the bus if the traction force of the engine is 15 kN? Express the answer in kN. What is the coefficient of friction?
The average height of the satellite above the Earth's surface is 900 km. Determine the speed of its movement.
Option 3.
Part A Choose one correct answer.
The parachutist descends vertically at a constant speed of 2 m / s. The frame of reference associated with the Earth is considered inertial. In this case:
1) no forces act on the parachute
2) the force of gravity is balanced by the force of Archimedes acting on the parachute
3) the sum of all forces acting on the parachute is zero
4) the sum of all forces is constant and not equal to zero
A body weighing 2 kg is acted upon by forces of 3 N and 4 N, directed perpendicular to each other. What is the acceleration of the body?
1) 3.5 m / s 2 2) 2.5 m / s 2 3) 7 m / s 2 4) 10 m / s 2
Satellite massT moves around the planet in a circular orbit radiusR... The mass of the planet M. which expression determines the value of the speed of the satellite?
1) 2) 3) 4)
The elevator is equipped with a spring balance on which a person stands. How will the scale readings change when the elevator moves up and down quickly?
1) up - increase, down - decrease
2) up - decrease, down - increase
3) up - will increase, down - will not change
4) up - will not change, down - will increase
A man was carrying a child on a sled along a horizontal road. Then a second child of the same type sat down on the sled, but the man continued at the same constant speed. How did the coefficient of friction change in this case?
1) did not change 2) increased 2 times
3) decreased by 2 times 4) increased by 50%
On an inclined plane, a bar is moving uniformly upward. Which vector shown in the figure is redundant or incorrect?
1) 2) 3) 4)
The vehicle speed module with a mass of 1000 kg changes in accordance with the graph shown in the figure. Which statement is correct?
1) on the aircraft section, the car was moving evenly
2) in section CDthe car was moving uniformly, the acceleration vector is directed opposite to the speed vector
3) on the siteEFthe car was at rest
4) the module of acceleration in the AB section is less than the module of acceleration in the sectionDE
Part B
Using the condition of the problem, match the equations from the left column with their graphs in the right column.
Three bodies of the same mass, 4 kg each, performed movements. The displacement projection equations are presented in the table. Which graph shows the dependence of the projection of the force on time, acting on each body?
Solve the problems.The lift descends with an acceleration of 2 m / s 2 ... In the elevator, a load weighing 0.7 kg hangs on a spring with a stiffness of 560 N / m. What is the spring force? How many centimeters did the spring lengthen?
The average height of the satellite above the Earth's surface is 600 km. Determine the speed of its movement.
Option4 .
Part A Choose one correct answer.
1) the lift falls freely
2) the lift rises evenly
3) the lift moves slowly up
4) the lift moves downward
Four forces act on a body weighing 2 kg. What is the acceleration of the body ifF 1 =12 H, F 2 =18 H, F 3 =20 H, F 4 =18 H.
1) 6 m / s 2 2) 16 m / s 2 3) 2 m / s 2 4) 4 m / s 2
The mass of the Moon is about 81 times less than the mass of the Earth. What is the ratio of the force of universal gravityF 1 acting from the Earth to the Moon, to the forceF 2 acting from the Moon to the Earth?
1)1/81 2) 81 3) 9 4) 1
How to force a 10 N weight to stretch the dynamometer spring with a force greater than 10 N?
1) move the dynamometer with the kettle down with some acceleration
2) move the dynamometer with a kettlebell upward with some acceleration
3) the dynamometer with a weight should fall freely
4) this is impossible
A man was carrying two identical children on a sled along a horizontal road. Then one child got up from the sled, but the man continued to move at the same constant speed. How to change the coefficient of friction in this case?
1) increased 2 times 2) decreased 2 times
3) increased by 50% 4) did not change
The bar is evenly moved up the inclined plane. Which vector shown in the figure is redundant or incorrect?
1) 2) 3) 4)
The vehicle speed module with a mass of 1000 kg changes in accordance with the graph shown in the figure. Which statement is correct?
1) in section CDthe car was moving uniformly, the acceleration vector coincides in direction with the speed vector
2) the module of acceleration in the AB section is greater than the module of acceleration in the sectionDE
3) on the siteDEthe car was moving uniformly accelerated, the acceleration vector is directed opposite to the speed vector.
4) on the AB section, the car moved evenly
Part B
Using the condition of the problem, match the equations from the left column with their graphs in the right column.
Three bodies of the same mass, 2 kg each, performed movements. The displacement projection equations are presented in the table. Which graph shows the dependence of the projection of the force on time, acting on each body?
Solve the problems.A car with a mass of 1 t moves with an acceleration of 0.8 m / s 2 ... A force of 2 kN is acting on the car? Determine the engine thrust (answer in kN) and the coefficient of friction.
The average satellite height above the Earth's surface is 300 km. Determine the speed of its movement.
Examination work No. 2
Dynamics.
DEMO VERSION
A1. The plane flies in a straight line at a constant speed at an altitude of 9 km. The frame of reference associated with the Earth is considered inertial. In this case:
1.the aircraft is not affected by any forces
2.the airplane is not affected by gravity
3.the sum of all forces acting on the plane is zero
4.the force of gravity is equal to the force of Archimedes, acting on the plane
A2. Four forces act on a body weighing 2 kg. What is the acceleration of the body if
F 1 = 20 H, F 2 = 18 H, F 3 = 20 H, F 4 = 16 H
A3. A satellite of mass m moves around the planet in a circular orbit of radius R. Mass of the planet M. What expression determines the value of the satellite's velocity?
A4. In order for the body in the elevator to experience overload (weight gain), it is necessary:
accelerated upward movement of the elevator
slow motion lift up
accelerated downward movement of the elevator
such a state is impossible
A5. A person was carrying a child on a sled along a horizontal road, then a second child of the same type sat down on the sled, but the person continued to move at the same constant speed, how did the friction force change?
has not changed
increased by 2 times
decreased by 2 times
increased by 50%
A6. The bar moves evenly up the inclined plane. Which vector shown in the figure is redundant or incorrect?
A7. The vehicle speed module with a mass of 1000 kg changes in accordance with the graph shown in the figure. Which statement is correct?
1.on the aircraft section, the car was moving evenly 
2.on the section DE the car was moving uniformly accelerated, the acceleration vector is directed opposite to the speed vector
3.on section AB, the car was moving evenly
4.the module of acceleration in section AB is less than the module of acceleration in section DE
IN 1. Three bodies of the same mass, 2 kg each, performed movements. The displacement projection equations are presented in the table. Which graph shows the dependence of the projection of the force on time, acting on each body? 
IN 2. A body weighing 10 kg suspended from the cable rises vertically. With what acceleration does the body move if the cable with a stiffness of 59 kN / m lengthened by 2 mm?
AT 3. The average height of the satellite above the earth's surface is 900 km. Determine the speed of his movement. (Give your answer in km / s)