Question

A bullet with a mass of 55 grams moving with a speed of 100 m/s slams into and wedges in a 1.9 kilogram block of wood supported by a string initially at rest. Which one, conservation of energy or conservation of momentum, can be applied to this situation? Why?

I think it's conservation of momentum because kinetic energy is not conserved in inelastic collisions. Correct?

Answer 1

Also, how high does the block swing after being hit by the bullet?

Answer 2

Actually, you can use the conservation of momentum first to find the initial velocity of the bullet-block system, and then you can plug that velocity into 1/2mv^2=mgh and solve for the height that the block swings, which gives a value of 0.403 m.

Correct?

Answer 3

Yes, that is exactly how to do the problem.

You are also correct that mechanical energy is not conserved.

Answer 4

Eureka!