Momentum and impulse — GCSE Physics practice questions

Question 1

In a game of pétanque, a player throws a metal boule of mass 700 g.
Just before it lands, the boule is moving at 5.0 m / s.

What is the momentum of the boule at this moment?

Accepted Answer

B: 3.5 kg m / s. Momentum = mass × velocity. The mass must be in kilograms: 700 g = 0.700 kg, so p = 0.700 × 5.0 = 3.5 kg m / s.

Question 2

Two magnetic pucks glide towards each other on an air table.
They collide, snap together and move off as one.

Which row describes the total momentum and the total kinetic energy of the pucks in the collision?

Accepted Answer

B: stays the same · decreases. With no external resultant force, the total momentum is the same after the collision as before. When the pucks stick together, some kinetic energy is transferred to thermal energy and sound, so the total kinetic energy decreases.

Question 3

During a hailstorm, hailstones hit a flat skylight at a rate of 0.60 kg per second.
They hit the skylight vertically at 12 m / s and bounce straight up at 4.0 m / s.

What is the average force exerted on the skylight by the hailstones?

Accepted Answer

D: 9.6 N. Each second, 0.60 kg of hail changes velocity from 12 m / s down to 4.0 m / s up, a change of 16 m / s. The rate of change of momentum is 0.60 × 16 = 9.6 kg m / s per second, so the skylight pushes the hail up with 9.6 N and the hail pushes the skylight down with 9.6 N.

	total momentum	total kinetic energy
A	stays the same	stays the same
B	stays the same	decreases
C	decreases	stays the same
D	decreases	decreases