A bullet of mass m is fired at a block of mass M hanging from a string. The bullet embeds itself in the block. This is an inelastic collision, in contrast to an elastic collision where energy is conserved. Is the initial momentum of the bullet equal to the momentum of the bullet plus the block immediately after the collision? YesNoInsufficient information to answerIs the initial kinetic energy of the bullet equal to the kinetic energy of the block plus bullet immediately after the collision? YesNoInsufficient information to answerIs the initial kinetic energy of the bullet equal to the gravitational potential energy of the block plus bullet at the top of the swing? YesNoInsufficient information to answer

Question

Coleman Hess

Physics

2 October, 18:36

A bullet of mass m is fired at a block of mass M hanging from a string. The bullet embeds itself in the block. This is an inelastic collision, in contrast to an elastic collision where energy is conserved. Is the initial momentum of the bullet equal to the momentum of the bullet plus the block immediately after the collision? YesNoInsufficient information to answerIs the initial kinetic energy of the bullet equal to the kinetic energy of the block plus bullet immediately after the collision? YesNoInsufficient information to answerIs the initial kinetic energy of the bullet equal to the gravitational potential energy of the block plus bullet at the top of the swing? YesNoInsufficient information to answer

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Hobbs · Answer 1

Answers:

Is the initial momentum of the bullet equal to the momentum of the bullet plus the block immediately after the collision? Yes

Is the initial kinetic energy of the bullet equal to the kinetic energy of the block plus bullet immediately after the collision? No

Is the initial kinetic energy of the bullet equal to the gravitational potential energy of the block plus bullet at the top of the swing? No

Explanation:

The main difference between elastic collision and inelastic collision is:

- In an elastic collision, both total momentum and total kinetic energy are conserved

- In an inelastic collision, the total momentum is conserved, while the total kinetic energy is not

In the problem, the collision is inelastic. According to these definitions, we can analyze each statement:

1) Is the initial momentum of the bullet equal to the momentum of the bullet plus the block immediately after the collision? Yes - -> in fact, we said that the total momentum is conserved also in an inelastic collision.

2) Is the initial kinetic energy of the bullet equal to the kinetic energy of the block plus bullet immediately after the collision? No - -> As we said, the total kinetic energy is not conserved in an inelastic collision.

3) Is the initial kinetic energy of the bullet equal to the gravitational potential energy of the block plus bullet at the top of the swing? No - -> Since the total kinetic energy is not conserved in the collision, some of it is lost, so the final gravitational potential energy of the block+bullet will be smaller than the initial kinetic energy of the bullet.