How Much Force Accelerates a Bullet in a Rifle?

[Emperor]

Homework Statement

A rifle bullet leaves the muzzle of a gun at 800. m/sec. The rifle barrel is 80. cm long and the mass of the bullet is 20.g. What force was needed to accelerate the bullet?

Homework Equations

Formulas:

F(Total)= ma

F= mg

F = micrometers (m)(g)

The Attempt at a Solution

t= 80 \div 800 = .1s

a= 800 - 0 \div .1 = 8000 m/s^2

The answer is provided on my sheet as 8000 N, but I don't have a clue as to how to do that. Its the closest I've gotten to the answer.

 

[Simon Bridge]

Welcome to PF;
The equation you used was for time assumed a constant speed along the barrel - but if the bullet travels at a constant speed, then the force must be zero.

if you imagine the bullet has constant acceleration from rest to 800m/s along the length of the barrel, then you use a kinematic equation to find the acceleration.

note: it is best practice to complete the algebra before using the numbers.

 

[Emperor]

Thanks for the help. Did you get the answer "8000 N" just like I did this time around?

 

[Simon Bridge]

I do not, as a rule, actually complete the problems here.
That's your job ;)

You'll find that the answer is not as important as your understanding of the physics behind it.