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Homework Help: Newton's 2nd Law & Inclined Ramp

  1. Nov 6, 2009 #1
    Well these two problems were from my quiz, and if I don't find out how to solve them soon, I'm going to spend my whole weekend thinking about them. D8 I'll try to remember the problems as best I can.

    1) An astronaut is in space, in the midpoint of two stars that have the same mass. If all other stars are an infinite space away, how much does the astronaut weight? Explain.

    2) A 75 kg box is on an inclined ramp that has an angle of 25 degrees. Its acceleration is 3.6 m/s/s.
    a) Find mu of k between the box and ramp.
    b) If the mass is 175 kg, what is its acceleration?

    The answers to #2 are (a) .061, (b) 1.54 m/s/s
    I just don't understand how to do part b. I got as far as finding sin, cos, and Fn, but I got stuck at finding Force of friction. I gave part a, just in case it's needed to solve b.
  2. jcsd
  3. Nov 7, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Please show your work and then we can see where you are getting stuck.

    For #2, part b presumably uses the same mu as you found in part a.
  4. Nov 7, 2009 #3
    Always use a free body diagram for the questions like 1.Where there is a force acting on something, so you can have a clear map of forces..
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