# Biophysics Problem 10

A $25\; kg$ mass is acted on by a constant 5 newton force. If the object started from rest, how far would it have travelled after 4 seconds?

#### First Step

I hope you realize that one of the first things you will have to do is use Newton's second law to find the acceleration of the object.

Calculate the acceleration.

Newton's second law states that:

$F = ma \\ \text{therefore,} \; a = F / m \\ = 5 \;N / 25\; kg \\ = 0.2\; m/s^2$

#### Variables

We now have a simple problem in kinematics. Make a list of the three variables you know and the one you don't know.

$u = 0 \\ a = 0.2 \;m/s^2 \\ t = 4\; s \\ s = ?$
Now go ahead and calculate '$s$'.
$s = ut + \frac{1}{2}at^2 \\ = 0 \times 4 + \frac{1}{2}\times 0.2 \times 4^2 \\ = 1.6 \; m$