Question

A block slides along a frictionless floor, then collides with a perfect spring attached to the wall. The spring compresses, and then its push sends the block sliding the other direction. Are momentum or energy conserved?

1) Energy and Momentum are conserved

2) Momentum is conserved, but not energy

3) Energy is conserved, but not momentum

4) Neither momentum nor energy are conserved

Two air hockey pucks are moving directly towards one another, but each with a different speed. After the collision, the two pucks have switched velocities. Are energy or momentum conserved?

1) Energy and Momentum are conserved

2) Momentum is conserved, but not energy

3) Energy is conserved, but not momentum

4) Neither momentum nor energy are conserved

A person jumps through the air, then lands on a skateboard and starts to roll forward. Consider only the horizontal component of momentum when answering. Are momentum or energy conserved?

1) Energy and Momentum are conserved

2) Momentum is conserved, but not energy

3) Energy is conserved, but not momentum

4) Neither momentum nor energy are conserved

I need help on this! can you also try to explain it??!!

Answer 1

For question 1, energy is conserved but momentum is not conserved since the net extenral force on the system is not zero (spring force is present)

In the second question, considering masses of the hockey pucks to be equal, both energy and momentum are conserved since the collision is elastic in nature.

In the third question, the momentum is conserved here as the external net force is zero on the system, but the collision is inelastic. Hence momentum is not conserved in this case