physics
posted by Rebecca .
A 25 g bullet traveling at 280 m/s passes completely through a wooden block, initially at rest on a smooth table. The block has a mass of 1000 g. The bullet emerges traveling in the same direction, but at 50 m/s. What percentage of total kinetic energy is lost in the process?

Find kinetic energy before, aka 1/2(mass of bullet)(velocity)^2. Then find the kinetic energy afterwards, which is 1/2(mass of bullet)(velocity afterwards)^2 + 1/2(mass of block)(whatever you got for part a)^2. Then divide whatever you got for the second part, divide it by the first part, and subtract the resulting decimal from 1 to find the percentage that was lost.