Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Energy: work with an inclination problem

  1. Jan 19, 2008 #1
    1. Karen has a mass of 52.9 kg as she rides
    the up escalator at Woodley Park Station of
    the Washington D.C. Metro. Karen rode a
    distance of 62.3 m, the longest escalator in
    the free world.
    The acceleration of gravity is 9.8 m/s^2 :
    How much work did the escalator do on
    Karen if it has an inclination of 34 degrees? Answer
    in units of J.

    2. Relevant equations

    3. The attempt at a solution i got the height to equal 34.83771789. i dunno if that helps or is needed.
  2. jcsd
  3. Jan 19, 2008 #2
    Ok. Now, you have the height. Whenever, a body is at a height, it has some 'Gravitational Potential Energy'. What is this energy in this case?
  4. Jan 19, 2008 #3
    does it have kinetic energy? be/c it doesnt say that she starts out at rest.
  5. Jan 19, 2008 #4
    i really dont know. i am very lost and frustrated.
  6. Jan 19, 2008 #5
    Whenever, a body is at a height, it has some 'Gravitational Potential Energy'. This is calculated as: [itex]E = mgh[/itex]. Where, 'm' is the mass of the object, 'g' is the acceleration due to gravity and 'h' is the height from the reference point (or level). When the body falls from this height to the reference level, it has the same energy the GPE. It is however converted to Kinetic Energy.

    The reference point is the point/level where you assume the potential energy to be zero. Here, the height 'h' is taken to be zero. We do this because, we can't really calculate potential energy (in classical mechanics atleast). We can only calculate the change in the potential energy when the body is moved somewhere.

    Here, take the ground as h = 0. Here we take the GPE as 0. After her height is increased by 'h', her GPE increases. By conservation of energy, it follows that this energy was supplied by the escalator, which we term as 'work' done by the escalator. So calculate this energy using the formula i have earlier.

    if u still have any doubts.. feel free to post.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook