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Homework Help: Ropes and Pulleys - Dynamics

  1. Oct 31, 2012 #1
    1. The problem statement, all variables and given/known data
    An environmentally-sensitive daredevil wants to use a large mass, a rope, and a pulley to accelerate toward ramp while his motorcycle is in neutral, as shown below. If friction is negligible, what will the acceleration of the motorcycle be and the tension of the rope?


    2. Relevant equations

    guy: Ft = ma

    weight: Ft - mg = ma

    I think....

    3. The attempt at a solution

    I don't know how to get acceleration because I don't know Ft...
    Last edited: Oct 31, 2012
  2. jcsd
  3. Oct 31, 2012 #2
    Does the question want you to calculate his accelerate on the ramp, or before it? Either way, you can't calculate tension right off the bat. The net force is going to equal the force of gravity on the 950kg mass. Divide that force by the system mass and you should get the acceleration before the ramp.
  4. Oct 31, 2012 #3
    I'm not sure, it just asks for acceleration, I still need help with this question.
  5. Oct 31, 2012 #4


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    Where does the 10 degrees come from? I don't see that in the question. If it's the slope of the ramp, that's not relevant. The question only asks you to consider circumstances before the ramp is reached, and nothing else is touching the ramp. The string is either horizontal or vertical.
    The most obvious way to approach the question (not necessarily the most elegant) is to consider the weight and the motorcycle-with-rider as two separate systems but with certain parameters in common. Each has a set of forces and an acceleration. Which of these do they share? Can you write down the free body equation for each?
  6. Oct 31, 2012 #5
    Sorry! The 10 degrees came from a different question, I looked off the wrong question, I've fixed it now.
  7. Nov 1, 2012 #6


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    Using the same m for both masses is going to be confusing. Use a different name for each different variable.
    Also, make sure you're measuring accelerations all in the same direction.
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