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Homework Help: Force vector problem

  1. Jul 21, 2009 #1
    1. The problem statement, all variables and given/known data
    A motorcycle and 67.0 kg rider accelerate at 3.2 m/s2 up a ramp inclined 10° above the horizontal.

    What is the magnitude of the force on the rider from the motorcycle?

    2. Relevant equations
    I set my 90 degree axis so that my x axis lined up with the acceleration up the ramp and my y axis lined up with the normal force. So my y component would be
    normal force-mass*gravity*cos 10° = mass*acceleration y

    3. The attempt at a solution
    I am thinking that the normal force is the force on the rider from the bike and with the way my axis is set up there will be no y acceleration so,

    normal force= mass*gravity*cos10°

    it gives and answer of 646.62 N but they say this answer is wrong. Am I missing something or misinterpreting?
  2. jcsd
  3. Jul 21, 2009 #2


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    Well, for some reason you are calculating only the normal force, when this is not what is being asked for.
  4. Jul 21, 2009 #3
    I'm sorry I didn't post the first question asked. Which was:
    (a) What is the magnitude of the net force on the rider?

    Which I found to be 214.4 N.

    I am missing something, What am I supposed to calculate? Isn't normal force the only force from the motorcycle onto the rider? My only other thought is including the acceleration caused by the bike.
  5. Jul 21, 2009 #4


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    No. If this were the case, why would the rider be accelerating up the ramp?
  6. Jul 22, 2009 #5
    I wasn't paying attention to the force from the motorcycle the accelerates the rider up the ramp. With that now understood I can take the normal force that I had found and use it as a y component and then find the force that the bike applies to the rider going up the ramp and use that as the x component on the rider. Solving for these two components should give me my magnitude of force on the rider from the bike.
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