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Calculating the energy in a part of a rollercoaster

  1. Sep 27, 2015 #1
    Hi(This thread might have been posted in the wrong section of the forum although this isn't a homework problem, just something I do because I like physics!), I've been trying to figure out how to solve this problem for a few hours, but whatever I do it seems to give me the wrong answer.

    Scale?geometry=300x300.jpg

    h(1)= 50m
    v= 0.5 m/s

    ## E = E_k + E_p ##
    Which gives me this formula
    ## E = \frac{1}{2}mv^2 + mgh ##
    After this I remove the mass since it's not been given in the task, and i'm left with:
    ## E = \frac{1}{2}v^2+ gh ##
    When I fill in the numbers I get this:
    ## E = \frac{1}{2}0.5^2 + 9.81*50 = 490 J ##

    But I'm supposed to get 49 J ?!

    Can't get any help from my teacher until tomorrow so would be lovely if some of you could tell me where I took a wrong turn(If I made a mistake)!

    Cheers,
    Lamefeed
     
    Last edited: Sep 27, 2015
  2. jcsd
  3. Sep 27, 2015 #2

    Nugatory

    User Avatar

    Staff: Mentor

    Something is wrong with the problem statement, because you need the mass. A grain of sand at the top of a 50 meter ramp represents a lot less potential energy than a brick at the top of the same ramp. You answer would be right if the cart had a mass of 1 kg, the book would be right if it had a mass of .1 kg, and yes, if you want more help with this problem you should start a thread in the homework section.

    This thread is closed; OP will restart in the HW section if necessary.
     
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