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Homework Help: Mass of an Object Moving Down a Slope.

  1. Nov 6, 2015 #1

    I am trying to find the magnitude of the resistance force of an object moving down a slope.
    The question I was given says:
    A skateboarder heads down a gentle slope (Θ=5°) at a constant speed of 5m/s. Calculate the magnitude of the resistance force.
    Using the equation mgSinΘ - ma = R, (g = 9.8, a = 0) I got as far as m0.854 = R, but I need m to find R.
    Is there another equation to find m (the mass of the object)?

    Any help would be much appreciated.
  2. jcsd
  3. Nov 6, 2015 #2


    Staff: Mentor

    What is R?
  4. Nov 6, 2015 #3
    R is the resistance force on the object (friction, air resistance etc.).

    Basically the forces going in the opposite direction to the skateboard.
  5. Nov 6, 2015 #4
    Distance, Height? Anything else given to you?
  6. Nov 6, 2015 #5
    Unfortunately no. Only the angle of elevation and speed of the object.
  7. Nov 6, 2015 #6


    Staff: Mentor

    Ah, ok. Then, if you're not given the mass of the object, ##mg \sin \theta## is the best you can do.
  8. Nov 7, 2015 #7
    Okay. Thanks for your help.
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