Question

A 10.1 g bullet leaves the muzzle of a rifle with a speed of 558.4 m/s. what constant force is exerted on the bullet while it is traveling down the 0.7 m length of the barrel of the rifle? answer in units of n

Answer 1

To answer any question to do with mass, acceleration, velocity (etc...) you use one or more of this set of equations. They are called the 'Kinematic' equations and are really easy to re-arrange, when you need to find the 'unknown quantity' that the question is asking for. Below these equations i will show you the general problem solving strategy to very quickly and easily solve these problems.

The Kinematic Equations

$D = (v_{i} * t) + (0.5 * a * t^2)$
$v_{f} ^2 = v_{i}^2 + (2 * a * D)$
$v_{f} = v_{i} + (a*t)$
$D = (\frac{v_{i} + v_{f}}{2} ) * t$

The Method

1. Write down all the known variables and their values + the one you don't know with a question mark next to it. (v = ?)

2. Find the kinematic equation where you have ALL the variables except the one you are missing.

3. Re-arrange the equation to solve for the missing variable.

Done!

HINT: Sometimes you need to use two kinematic equations, one after the other, in order to get the answer. It is common for questions to not give two variables, like velocity AND acceleration to force you to solve for one, then use that solution in another kinematic equation to finally solve the problem. Writing down the known variables is the fastest way to see what you have and what you need.
____________________________________________

This question takes things one step further and is asking you to find the FORCE on the bullet. To convert to a force in any situation you need to find the acceleration and multiply it by the mass as follows:

$F = m * a$

Remember this equation!! you will use it ALL the time.

Please let me know if you still cannot solve this problem, but i believe you should be fine :)