Question

An 8 g bullet is shot into a 4.0 kg block, at rest on a frictionless horizontal surface. The bullet remains lodged in the block. The block moves into a spring and compresses it by 9.4 cm. The spring constant is 1000 N/m. What is the initial velocity of the bullet?

Answer 1

Figure the energy stored in the spring. Now give that energy to KE of the block after impact. Now find the initial velocity of the block. Now set the initial momentum of the block equal to the bullet. find velocity of bullet.

Answer 2

1/2K(x^2)=1/2(M bullet+M block)(v^2)
1/2*(1000N/m)*(0.094^2)=1/2(0.008kg+4kg)(v^2)

V=Sqrt (4.418/2.004)
V=1.48 m/s