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Force vectors help

  1. Sep 22, 2011 #1
    1. The problem statement, all variables and given/known data
    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 do not know how to calculate the acceleration, please help and explain. Thanks in advance.

    *I figured out the horizontal acceleration, but how do you know which direction it goes? Left or right?
    Last edited: Sep 22, 2011
  2. jcsd
  3. Sep 22, 2011 #2


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    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.
  4. Sep 22, 2011 #3
    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?
  5. Sep 22, 2011 #4


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    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 ____.
  6. Sep 27, 2011 #5
    Thank you! This is now starting to make sense!
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