Calculating force on a bullet, given mass + velocity + barrel length

[exi]

Homework Statement

An 8.9 g bullet leaves a rifle's muzzle at 456.6 m/s. The barrel is 0.5 m long.

What is the force exerted on the bullet as it travels the length of the barrel? Answer in N.

Homework Equations

F = ma
V = d/t (so T = d/v)
a = v/t

The Attempt at a Solution

I tried to do this:

1: T = d/v = 0.5 m / 456.6 m/s = 0.0011 s
2: A = v/t = 456.6 m/s / 0.0011 s = 416967.12 m/s^2
3: F = ma = 0.0089 kg * 416967.12 m/s^2 = 3711.0073 (kg∙m)/s^2

No love.

Anyone see anything glaringly wrong?

 

[Doc Al]

1: T = d/v = 0.5 m / 456.6 m/s = 0.0011 s

The speed is not constant.

 

[Astronuc]

leaves a rifle's muzzle at 456.6 m/s.

So 456.6 m/s is the exit velocity, and the bullet started at zero velocity.

Now what is it about force applied over distance, and what is the change in kinetic energy?