Question

A bullet of mass 0.010 kg and speed of 100 m/s is brought to rest in a wooden block after penetrating a distance of 0.10 m. The work done on the bullet by the block is

so my answer is 50 but I'm getting it wrong? I don't understand why??
work=KE 1/2(.010)(100)^2=50!

Answer 1

well how do I figure how much work the wood block did on the bullet??

Answer 2

The work done is force times distance and that is 500 * 0.1 = 50 Joules which is what you had and I believe is correct either way you do it.

Answer 3

Ok so my professor FINALLY responded to me and said the answer is -50 J not 50J with no explanation.
What variable would I make negative to produce that answer? Would the velocity by negative since the wood is stopping the bullet?

Answer 4

Yes.
Went you slow something down your force is opposite to the velocity, you remove kinetic energy, negative work

Answer 5

ok! finally some clarity. thank you!

Answer 6

V^2 = Vo^2 + 2a*d = 0,
V^2 = 100^2 + 2a*0.1 = 0,
a = -5*10^4 m/s^2.

F = M*a = 0.01 * (-5*10^4) = -500 N.
W = F*d = -500 * 0.1 = -50 J.