posted by Fred on .
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?
Also, how high does the block swing after being hit by the bullet?
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.
Yes, that is exactly how to do the problem.
You are also correct that mechanical energy is not conserved.