Question

Please help, I'm kinda stuck on this one.
A 4-g bullet is fired horizontally with a speed of 300m/s into a 0.8 kg block of wood at rest on a table. If the coefficient of friction between the block and the table is 0.3 , how far will the block slide? What fraction of the bullet’s energy is dissipated in the collision itself?

Answer 1

1 compare total **momentum** just before and just after the collision, ie before the block starts moving. assume that the bullet and block become one moving body with a combined mass. that will give you initial instantaneous velocity of the combined bullet and block.


2 compare (kinetic) energy of block at that instant, once bullet and block have combined. then assume all that energy disappears (into heat) as work 'W' done by friction whilst the combined bullet & block travels a distance 'x'. W = F*x and F = mu R (friction). that will give you x.

3 finally, the bullet's energy will equal the energy of the combined bullet and block immediately they collide PLUS any energy that is lost on collision. you have the numbers you need to make that calculation.

if this is not clear, pls circle back.....:p