Pushing a box up a ramp a certain distance - work

  1. 1. The problem statement, all variables and given/known data

    A horizontal 25 N pushing force acts on a 10 kg crate moving up a ramp. The ramp is inclined at 37 degrees above the horizontal.

    How much work is done by this force in moving the crate a distance of 15m along the ramp?

    2. Relevant equations

    W = Fd

    3. The attempt at a solution

    This was on a previous test i took and i got it wrong and now looking over it again i cannot seem to figure it out.

    I thought i could take the component of the pushing force parallel to the ramp and subtract the component of the weight of the block that is parallel to the ramp then just multiply that by the distance but that didnt work out to well.

    here is was i did

    The component of the pushing force parallel to the ramp is

    25cos(37) = 19.96

    the component of the weight parallel to the ramp (and opposite in direction of the component of the pushing force parallel to the ramp) is

    mgsin(37)

    10(9.8m/s^2)sin(37) = 58.9

    so subtract those two

    19.9 - 58.9 = - 39N

    so W = 39N(15m)

    W = 585 J

    the correct answer is 300 J

    Any help would be great.

    Thank you :)
     
  2. jcsd
  3. PhanthomJay

    PhanthomJay 6,253
    Science Advisor
    Homework Helper
    Gold Member

    Chegg
    You are calculating the work done by the pushing force and gravity (and you left out the minus sign). But the problem asks for the work done by the pushing force only.
     
  4. oh so since its just the work done by the pushing force, i dont even have to factor in the other forces. Got it.

    If it would have asked how much work does it take to move the block 15 m then would that mean i would have to factor in the other forces like i did in my first post?

    I just feel like i dont know when i would have to consider the forces of the weight of the block being pushed.
     
    Last edited: May 8, 2010
  5. If this problem would have asked for the total work required to push the block up the ramp 15 m then would i have had to consider in the force of gravity like i did in my first post?
     
  6. PhanthomJay

    PhanthomJay 6,253
    Science Advisor
    Homework Helper
    Gold Member

    You'd have to consider the work done by all forces to calculate the total work done on the block. In your example, the block would not move up the ramp if there were no other forces acting besides the pushing force and the block's weight, so there has to be anothner force acting (not given) to move it up.
     
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