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Which requires less force?

  1. May 26, 2012 #1
    1. The problem statement, all variables and given/known data

    Which requires less force?
    -pushing an object 1.2m over a rough surface
    -lifting an object to a height of 1.2m
    -pushing an object 1.2m over a smooth surface
    -lifting an object to a height of 1.2m using an inclined plane


    2. Relevant equations

    F=ma

    3. The attempt at a solution

    Pushing an object over a rough surface is going to require more force since friction is opposing the applied force. Lifting the object directly upwards is going to involve gravity soo.. im down to pushing over a smooth surface or lifting using an inclined plane. My guess for the answer to this question is currently pushing over a smooth surface since there is not much friction involved.
     
  2. jcsd
  3. May 26, 2012 #2
    Hi. Unfortunately, we need more information that is provided.

    It is very likely that the coefficient of kinetic friction could make it so that the work done to move along the rough surface is greater than that required to move the object against gravity.

    I do not want to completely solve the problem, but I will give a few important points:
    1. Moving with friction obviously involves more work than without friction (and since W=F*d, more force).
    2. If the inclined plane is frictionless, the same amount of work is required to move it up the plane as directly up. Gravity is a conservative force, so it doesn't matter if you go directly up, or "sideways." Gravity will still do the same amount of negative work, and so the same amount of force will be required (again, W=f*d).
     
  4. May 26, 2012 #3
    1-pushing an object 1.2m over a rough surface
    2-lifting an object to a height of 1.2m
    3 -pushing an object 1.2m over a smooth surface
    4-lifting an object to a height of 1.2m using an inclined plane

    1. if μ=1, frictional force =mg
    2 gravitional force=mg
    3. μ<1, frictional force <mg
    4. less gravitional force + frictional force.
     
  5. May 26, 2012 #4
    Hmm, now that I think of it, I might have been mistaken about the inclined plane. While it is true that the work done by gravity will be the same, it is also true that the force required to move it up the ramp will be less because the distance will be greater.

    Regarding the other problem with the friction, since values are not give, we cannot solve the problem. Depending on the coefficient of kinetic friction, either moving up or moving over the surface could require a greater force.
     
  6. May 26, 2012 #5
    Alright thanks for trying to help me out with this one. It was a question that I recently answered on a worksheet that was due for class. I ended up picking "pushing an object over a smooth surface" that seemed the most logical.

    *I was really curious after I handed it in, twas why I have posted here
     
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