# Homework Help: Joules from Newtons?

1. Jul 12, 2015

How much work is done by the force?
W= F * Δs * Cosθ

W= (152N) * (13m) * Cos(33°)
W=1976 * Cos(33°)
W=1657.2

So I'm fairly confident I got this right since the answer is 1660J my question is Why would I have to round it up to 1660 to get it to Joules? I'm not really looking for help on the answer just an explanation as to WHY? Any help would be appreciated!

2. Jul 12, 2015

### Engineer at UIC

It's already in joules. When you multiply force by distance,
W=F*d*cos(theta)
Joules = Newtons * meters * [no dimensions for trig]

3. Jul 12, 2015

ok but why the rounding to 1660 from 1657? That is kind of confusing to me so i really want to know to make sure im not missing anything important.

4. Jul 12, 2015

### Engineer at UIC

You can only answer with as many significant figures as you're given. 1657 is 4 significant figures, but your force only had three.

5. Jul 12, 2015

Oh... that makes a lot of sense! Thank you for your help!!

6. Jul 12, 2015

### SteamKing

Staff Emeritus
The force has three sig figs, but I believe the distance the box was moved (13 m) only has two.