1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Energy Required to Lift a Heavy Box

  1. Mar 11, 2005 #1
    As you are trying to move a heavy box of mass [tex]m[/tex], you realize that it is too heavy for you to lift by yourself. There is no one around to help, so you attach an ideal pulley to the box and a massless rope to the ceiling, which you wrap around the pulley. You pull up on the rope to lift the box.


    A.) What is the magnitude [tex]F[/tex] of the upward force you must apply to the rope to start raising the box with constant velocity?
    Express the magnitude of the force in terms of [tex]m[/tex], the mass of the box.


    I think the answer should be mg/2

    is this correct?
     
  2. jcsd
  3. Mar 11, 2005 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Yes. The pulley gives you a mechanical advantage, reducing the force (but not the energy!) needed to lift the box.
     
  4. Mar 11, 2005 #3

    James R

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    The pulley won't make it any easier. The force you'll need to apply with a single pulley is still F=mg.

    ...

    Edit: Hmm... I think I might have mistaken the way the pulley is connected, in which case the force may be mg/2. A diagram would be nice!
     
  5. Mar 12, 2005 #4
    With a single pulley the way you described it there's no way to shorten the distance over which the force is applied (it is the same as the distance over which the pulley rises). So the force is still mg. The only facilitation is that you apply the force downward.
     
  6. Mar 12, 2005 #5

    Doc Al

    User Avatar

    Staff: Mentor

    Please reread the original post: The pulley is attached to the box, not the ceiling.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Energy Required to Lift a Heavy Box
Loading...