A hockey puck sliding on a frictionless surface strikes a box at rest. After the collision, the two objects stick together and move at some final speed. Which of the statements describes the change in momentum and energy of the puck during the collision?

a. puck loses some but not all of its original momentum.
b. one cannot determine
c. puck conserves original momentum, but loses all mechanical energy
d. puck loses some momentum but conserves mechanical energy
e. puck loses conserves all momentum and mechanical energy
f. conserves momentum but loses some mechanical energy

Which of the following describes the change in momentum and energy of the combined puck and box?

a. system loses some but not all of its original momentum.
b. one cannot determine
c. system conserves original momentum, but loses all mechanical energy
d. system loses some momentum but conserves mechanical energy
e. system loses conserves all momentum and mechanical energy
f. conserves momentum but loses some mechanical energy

Explanation:

1)

As we will consider the puck only as our system then during the collision with the box the normal force during the time of collision will behave like external force on the puck

So as per Newton's II law we know that

so momentum of the puck is not conserved

Also we know that puck and the box both stick together so this is inelastic collision

So here we can say that energy of puck is lost during the collision

so correct answer will be

a. puck loses some but not all of its original momentum.

2)

When we will consider the box + puck as our system then the force between puck and the box is internal force of the system

and since there is no external force on it

So the momentum of the system is conserved

But here we know that the collision between them is inelastic collision so here mechanical energy is not conserved

so correct answer here will be

f. conserves momentum but loses some mechanical energy

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