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A greyhound runs along a straight track.
Write down the equation that links momentum, mass and velocity.
Give the unit of momentum.
The greyhound has a mass of 32 kg and runs at a velocity of 15 m/s.
Calculate the momentum of the greyhound.
Momentum = ................................ kg m/s
A student pushes a loaded supermarket trolley along a level floor.
State what is meant by 'conservation of momentum' in a closed system.
The trolley and its contents have a total mass of 18 kg.
The momentum of the trolley and its contents is 45 kg m/s.
Calculate the velocity of the trolley.
Velocity = ................................ m/s
A student investigates collisions using two trolleys on a level track.
Trolley A has a mass of 0.80 kg and moves to the right at 0.50 m/s.
Trolley B has a mass of 1.20 kg and is at rest.
The trolleys stick together when they collide.
Calculate the momentum of trolley A before the collision.
Momentum = ................................ kg m/s
The trolleys move off together after the collision.
Calculate the velocity of the trolleys immediately after the collision.
Velocity = ................................ m/s
The collision between the trolleys takes 0.15 s.
Calculate the average force exerted on trolley B during the collision.
Use the Physics Equations Sheet.
Average force = ................................ N
Two students stand facing each other on skateboards on a smooth, level floor. Both students are at rest.
The students push each other and move apart.
Student X has a mass of 45 kg and moves to the left at 1.2 m/s.
Student Y has a mass of 60 kg.
State the total momentum of the two students before they push each other.
Calculate the velocity of student Y immediately after the push.
Give the direction of the velocity.
Velocity = ................................ m/s
Direction = ................................
A gymnast lands on a thick crash mat after dismounting from a beam.
The gymnast has a mass of 48 kg and is moving downwards at 6.0 m/s when she first touches the mat.
The crash mat brings the gymnast to rest in 0.60 s.
Calculate the average force exerted on the gymnast by the crash mat.
Use the Physics Equations Sheet.
Average force = ................................ N
Explain how the crash mat reduces the risk of injury to the gymnast compared with landing on the bare wooden floor.
The table gives the mass and the velocity of three moving objects.
| Object | Mass in kg | Velocity in m/s |
|---|---|---|
| tennis ball | 0.058 | 45 |
| cyclist and bicycle | 85 | 8.0 |
| car | 1200 | 30 |
Calculate the momentum of the cyclist and bicycle.
Momentum = ................................ kg m/s
A bullet of mass 0.012 kg has the same momentum as the tennis ball in the table.
Calculate the velocity of the bullet.
Velocity = ................................ m/s
The car in the table is brought to rest in a crash test. The car takes 0.12 s to stop.
Calculate the average force acting on the car as it stops.
Use the Physics Equations Sheet.
Average force = ................................ N
A football of mass 0.44 kg is kicked horizontally at a wall.
The ball hits the wall at 12 m/s and rebounds horizontally at 8.0 m/s.
Calculate the magnitude of the change in momentum of the football.
Change in momentum = ................................ kg m/s
The ball is in contact with the wall for 0.050 s.
Calculate the average force exerted on the ball by the wall.
Use the Physics Equations Sheet.
Average force = ................................ N
A second ball of the same mass hits the wall at 12 m/s but does not rebound. It is brought to rest in the same contact time of 0.050 s.
Explain why the average force on this ball is smaller than the force calculated in part (b).
A car is used in a crash test. The car travels at 14 m/s and hits a solid barrier.
A crash-test dummy of mass 75 kg is strapped into the driver's seat. The dummy is brought to rest by the crash.
Show that the change in momentum of the dummy is about 1000 kg m/s.
In the first test the car has no air bag. The dummy is brought to rest in 0.070 s.
Calculate the average force on the dummy.
Use the Physics Equations Sheet.
Average force = ................................ N
Safety regulations state that the average force on the dummy must not be greater than 5000 N.
Calculate the minimum time over which an air bag must bring the dummy to rest to meet this regulation.
Time = ................................ s
The test is repeated at the same speed using a dummy of greater mass.
The air bag brings this dummy to rest in the same time as before.
Explain why the average force on this dummy is greater.