# Physics

• Sep 25th 2012, 04:47 PM
Louisana1
Physics
Three forces act on an object. A 3 N force acts due east and a 6 N force acts due north. If the net force on the object is zero, what is the magnitude of the third force?

What is the equation for this? I have been trying to work this out for 40mins?
• Sep 25th 2012, 04:56 PM
skeeter
Re: Physics
$\sum F_x = 0$

$\sum F_y = 0$

you have a 3N force east ... has to be balanced by a 3N force west

you have a 6N force north ... has to be balanced by a 6N force south

this says the 3rd force has a west component of 3N and a south component of 6N ... resolve the components.
• Sep 25th 2012, 05:06 PM
Louisana1
Re: Physics
Skeeter do you know where I can find a video or examples like this problem? I am like totally lost.
• Sep 25th 2012, 05:34 PM
skeeter
Re: Physics
• Sep 26th 2012, 09:42 AM
Louisana1
Re: Physics
I still got stuck on this problem so I asked the instructor, but no help really he was pretty busy. He did give me this but have no clue how he got it.

A+B magnitude = sqrt(6^2 + 3^2) = 6.71

How the heck did he get this? I am putting the numbers in the calculator and not coming up with 6.71
• Sep 26th 2012, 12:56 PM
skeeter
Re: Physics
he's using Pythagoras ... and you must be entering the info in your calculator incorrectly

$\sqrt{6^2+3^2} = \sqrt{36+9} = \sqrt{45} \approx 6.71$