N's Laws of Physics?

Question

A 4.90 g bullet leaves the muzzle of a rifle with a speed of 317 m/s. The expanding gases behind it exert what force on the bullet while it is traveling down the barrel of the rifle, 0.800 m long? Assume constant acceleration and negligible friction

Answer 1

W = Fd = 1/2 mv^2 = KE kinetic energy at the muzzle; where W is the work on the bullet with mass m = .0049 kg while it travels the d = .8 m barrel under force F and exits at the muzzle with velocity v = 317 m/sec

Solve for F = mv^2/2d and you have your answer. All the factors on the RHS of = are given. You can do the math.

The physics lesson is this. The work put into the bullet going down the barrel is converted to kinetic energy at the muzzle. This is consistent with the conservation of energy and work is a form of energy. Thus work is converted to KE; so that W = KE.