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Mechanics · Part 3 of 3
18 exam-style questions with model answers, plus 24 quick multi-choice questions — every question on this part of the standard, grouped by the 6 pages of notes they come from.
Write a full answer before you reveal the model one. That comparison is where the learning happens.
A kg runner moves at m s−1.
Calculate the runner's momentum.
A kg tennis ball travelling at m s−1 is struck by a racquet and returns along the same line at m s−1.
Calculate the change in momentum of the ball, and explain why the change is larger than the momentum the ball had before being struck.
Two identical kg trolleys approach each other along a track, each travelling at m s−1.
Calculate the total momentum and the total kinetic energy of the system. Then explain fully why the total momentum can be zero while the kinetic energy is not, and what this means for what happens when they collide head-on and stick together.
A force of N acts on an object for s.
Calculate the impulse delivered to the object.
A kg cricket ball travelling at m s−1 is caught and brought to rest in s.
Calculate the average force exerted on the ball, and explain why a fielder moves their hands backward while catching.
A kg stunt performer falls from a height and lands at m s−1. In one take she lands on a crash mat and stops in s; in another she lands on bare concrete and stops in s.
Calculate the average force in each case. Explain fully, using impulse, why the crash mat protects her, and explain why bending the knees on landing has the same effect. Include a comment on why a bouncing landing would be worse than one where she comes to rest.
A kg trolley moving at m s−1 collides with a stationary kg trolley and they stick together.
Calculate their common velocity after the collision.
A kg ball moving east at m s−1 collides with a kg ball moving west at m s−1. They stick together.
Calculate their velocity after the collision, and state with a reason whether the collision is elastic or inelastic.
A kg railway wagon rolling at m s−1 couples with a stationary kg wagon.
Calculate the velocity after coupling and the kinetic energy before and after. Explain fully why momentum is conserved but kinetic energy is not, referring to Newton's third law and to where the energy goes.
A kg skater standing at rest on ice pushes a kg ball away at m s−1.
Calculate the skater's recoil velocity.
A kg cannon fires a kg shell horizontally at m s−1.
Calculate the recoil velocity of the cannon, and explain why the cannon recoils much more slowly than the shell travels.
Two ice skaters, of mass kg and kg, stand at rest facing each other and push apart. The lighter skater moves off at m s−1.
Calculate the heavier skater's velocity and the total kinetic energy after the push. Explain fully why the total momentum is zero both before and after, while the kinetic energy increases from zero, and state where that energy came from.
A force of N pushes a box m across a floor in the direction of the force.
Calculate the work done.
A kg student runs up a flight of stairs m high in s.
Calculate the work done against gravity and the student's power output. Explain why a second student who climbs the same stairs in s does the same work but has half the power.
A kg car travels at a constant m s−1 along a level road against total resistive forces of N. It then climbs a hill that rises m for every m travelled along the road, maintaining the same speed and facing the same resistive forces.
Calculate the engine power required in each case. Explain fully why more power is needed on the hill even though the speed is unchanged, and explain why the car has zero acceleration in both cases despite the engine working hard.
A kg object moves at m s−1.
Calculate its kinetic energy.
A kg ball is dropped from a height of m and rebounds to a height of m.
Calculate the energy transformed into heat and sound during the bounce, and explain why the ball does not return to its original height.
A kg skateboarder starts from rest at the top of a ramp m high. She reaches the bottom at m s−1.
Calculate the energy transformed by friction and air resistance, and the speed she would have reached without them. Explain fully why the energy method gives the final speed without any knowledge of the ramp's shape, and explain why the equations of motion could not be used here.