The net force performs a total amount of work equal to
(45 N) (0.80 m) = 36 J
on the bullet, and this is in turn is equal to the change in the bullet's kinetic energy by the work-energy theorem. So we have
W = ∆K = 1/2 mv²
since the bullet starts at rest, where m = its mass and v = its final velocity.
Solve for v :
36 J = 1/2 (0.0050 kg) v² ⇒ v = 120 m/s
