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!

Gravitational potential energy.

  1. Nov 23, 2008 #1
    1. The problem statement, all variables and given/known data
    Hey guys, just wondering if you guys could help me out a bit.

    A boy on a sled with a total mass of 72kg slides from rest down a hill, which is 35m high. The friction force between sled and snow has a magnitude of 250N. If the slope of the hill makes an angle of 37 degrees with the horizontal, find:
    a) the gravitational potential energy of the sled at the top of the hill relative to the base.

    2. Relevant equations

    If i am not mistaken the equation for Gav.pot energy is
    U= GMe * m

    and the value of g can be found as g = G * Me/ (R + h)2

    3. The attempt at a solution

    I know i have the following from the question:

    m= 72kg
    Ff= 250N

    now what i dont get is where the 37 degrees is supposed to come in and i am not quite sure that that is the equation that i am supposed to use. Could someone please explain to me how i would begin this question? I want to solve it my slef but can someone point me in to a direction. thank you.

    edit: wait a second, i think i was doing it wrong. Would it be like E1g = mgh = (72kg)(9.8m/s2)(35m) = 24696 J ?
    Last edited: Nov 23, 2008
  2. jcsd
  3. Nov 23, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Much simpler would be to use PE = mgh, which is perfectly good near the Earth's surface.

    Maybe you don't need it for part a. :wink:
  4. Nov 23, 2008 #3

    Doc Al

    User Avatar

    Staff: Mentor

    Now you've got it.
  5. Nov 23, 2008 #4

    Ok cool thanks guys, i think i can handle it form here ^_^. look like i will be studying all day for that physics test tomorrow :frown:
  6. Nov 23, 2008 #5
    Sorry for posting again but now i am stuck at part c of the question which is : the speed of the sled at the bottom of the hill.

    How would i find this out? I know i have to use the 37 degrees somehow but i am stuck, I now have the following variables.

    h1 = 35m
    Ff = 250N
    gav.pot energy : 24696J
    Work: 8750J

    Its been a while since i have had to find speed so a hint would be helpful =)
  7. Nov 23, 2008 #6

    Doc Al

    User Avatar

    Staff: Mentor

    What's the work done by friction? Hint: What's the distance traveled by the sled?

    Set up an energy equation.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Gravitational potential energy.