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Homework Help: TORQUE help!

  1. Dec 4, 2005 #1
    1.) A mechanic jacks up a car to an angle of 8.0° to change the front tires. The car is 3.20 m long and has a mass of 1160 kg. Its center of mass is located 1.12 m from the front end. The rear wheels are 0.40 m from the back end. Calculate the torque exerted by the car around the back wheels.
    --I'm not sure how to set this up. I know the equation for torque is t=fr sin(theta)

    2.) A bucket filled with water has a mass of 71 kg and is attached to a rope that is wound around a 0.035 m radius cylinder. A crank with a turning radius of 0.15 m is attached to the end of the cylinder. What minimum force directed perpendicularly to the crank handle is required to raise the bucket?
    --I think this is a moment of inertia problem... so for that shape it would be MR^2 but after you find that what would you plug that into?
  2. jcsd
  3. Dec 4, 2005 #2


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    1) The force you should consider is gravity. You can act as though the gravitational force acts solely at the center of mass.
    You should know what F is. An angle and r are also given. Draw a diagram if necessary.

    2) No mass is given for the cylinder or crank so I`m not sure you should consider the moment of inertia, although the question doesn't mention about neglecting it. You should calculate the torque necessary to keep the bucket in place, so that the total force acting on it is zero.
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