# Homework Help: Force vectors help

1. Sep 22, 2011

### MakeItThrough

1. The problem statement, all variables and given/known data
http://www.webassign.net/CJ/04_11.gif
Two forces, F1 and F2, act on the 5.00-kg block shown in the drawing. The magnitudes of the forces are F1 = 30.0 N and F2 = 45.5 N. What is the horizontal acceleration (magnitude and direction) of the block? Direction... Left or Right?

2. Relevant equations
F = mass x acceleration
acceleration = F / Mass

3. The attempt at a solution
I got two x and y components:
F1x = cos65 x 30 = 12.68 N
F1y = sin65 x 30 = 27.19 N

*I figured out the horizontal acceleration, but how do you know which direction it goes? Left or right?

Last edited: Sep 22, 2011
2. Sep 22, 2011

### PhanthomJay

Theer are a couple of other forces in the y direction not shown, but that block isn't going anywhere in the y direction, so you need not concern yourself with y direction forces in this problem . You have F1x correct, what about F2x? Then look in the x direction using newton's 2nd law to solve for the acceleration (magnitude AND direction) in the x direction.

3. Sep 22, 2011

### MakeItThrough

ahh I figured it out. F1x is 12.68 N and F2 is 45.5 N. I just subtract 12.68 from 45.5 and that gives me 32.82 N. The mass of 5 kg is given.
Plugging this into the formula F=ma
32.82 / 5 kg = 6.564 m/s^2.
However, I'm not sure which direction the horizontal acceleration goes. Left or Right? How can you tell?

4. Sep 22, 2011

### PhanthomJay

The acceleration is always in the direction of the net force. Since F2 is greater than the horizontal component of F1, then the horizontal net force acts to the ____ and thus the acceleration is to the ____.

5. Sep 27, 2011

### MakeItThrough

Thank you! This is now starting to make sense!
(left)