Momentum problem

Question

Imagine two pucks sitting on level ice. Both pucks are pushed by identical forces across the ice over 3m. While both pucks start at rest, puck A is twice as massive as puck B. Which puck has a large change of momentum after it is pushed the 3m? Select the best answer

A. Puck A since it will take longer to go the 3m

B. It’s a tie. Both pucks have the same initial momentum of 0kg m/s

C. They both have the same change of momentum since they experience the same force over the same distance of 3m

D. Puck A since the final momentum is calculated by multiplying its larger mass by the same final velocity as puck B.

E. Puck B since it will be moving faster at 3m

F. Puck B since it accelerates more than pick A due to its smaller mass.

Answer 1

Going though the options one by one:

a) Correct. For a force that is constant over time, the change in momentum is given by L = F t. Block A has more mass, which means it has more resistance to changes in its motion, so it will take longer to travel 3m, so both t_a and L_a will be greater.

b) False, both pucks are being acted on by an exterior force, so their initial momentum has no bearing on their final momentum.

c) False, the same force acting over the same distance means that they will have the same kinetic energy, not linear momentum.

d) False, because they will have the same final kinetic energy, but different masses, their final velocities will be different.

e) False, if one performs work-energy analysis on the two pucks, it can be shown that the increased velocity of puck B does not make up for the higher mass of puck A.

f) False, again, the heightened acceleration is not enough to produce a final velocity for puck B that overcomes the weight difference.