Elastic vs. Inelastic Collisions

[G1SG2]

Suppose you shot a bullet into a stationary block. Which of the following would lead to a smaller final block speed:

I. Giving the bullet a smaller initial speed
II. Using a heavier block
III. Having an elastic as opposed to an inelastic collision
IV. Using a lighter bullet

A. I only
B. I, II, III & IV
C. I, II, & IV
D. III only

I chose C, which is the correct answer. My question is-does III not affect the block speed at all? I know it won't result in a smaller block speed, but would it lead to an increased block speed since in an elastic collision, the block would be moving by itself and would have less inertia, a greater relative acceleration, and a greater v?

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[Pulsar]

Suppose you shot a bullet into a stationary block. Which of the following would lead to a smaller final block speed:

I. Giving the bullet a smaller initial speed
II. Using a heavier block
III. Having an elastic as opposed to an inelastic collision
IV. Using a lighter bullet

A. I only
B. I, II, III & IV
C. I, II, & IV
D. III only

I chose C, which is the correct answer. My question is-does III not affect the block speed at all? I know it won't result in a smaller block speed, but would it lead to an increased block speed since in an elastic collision, the block would be moving by itself and would have less inertia, a greater relative acceleration, and a greater v?

I and IV are correct because there's less energy in the system to work with. II is correct because the velocity of the heaver block after the energy is transferred to it must be less (since KE = 1/2mv^2).

An elastic collision is one in which ALL KE is conserved. An inelastic collision is a collision in which some of the KE is being converted into some other form of energy (possibly heat). If the "original" collision was inelastic, as suggested by choice III, then it means some of the energy was lost (and not put towards moving the block). If in the second trial we make it an elastic collision, it means all the energy that was lost to heat can now be put towards moving the block (which will always make it move faster).

 

[G1SG2]

I and IV are correct because there's less energy in the system to work with. II is correct because the velocity of the heaver block after the energy is transferred to it must be less (since KE = 1/2mv^2).

An elastic collision is one in which ALL KE is conserved. An inelastic collision is a collision in which some of the KE is being converted into some other form of energy (possibly heat). If the "original" collision was inelastic, as suggested by choice III, then it means some of the energy was lost (and not put towards moving the block). If in the second trial we make it an elastic collision, it means all the energy that was lost to heat can now be put towards moving the block (which will always make it move faster).

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