Torque crank and bucket question

  • Thread starter dnt
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dnt

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1. The problem statement, all variables and given/known data

A bucket filled with water has a mass of 70 kg and is attached to a rope that is wound around a 0.035 m radius cylinder. A crank with a turning radius of 0.35 m is attached to the end of the cylinder. What minimum force directed perpendicularly to the crank handle is required to raise the bucket?

2. Relevant equations

obviously torque = F * r * sin

3. The attempt at a solution

my problem here is i cannot accurately understand the diagram (there is no picture that goes along with it). i cannot tell which r value to use. if someone could clarify that i would appreciate it.
 

Doc Al

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This is really an equilibrium problem: the bucket (via the rope) exerts a tension on the cylinder tending to make it turn one way; you (via the crank handle) have to exert a torque in the opposite direction to balance it out.

I was able to dig up a diagram that will help you visualize what's going on. Go to http://www.physics.utah.edu/~woolf/2010_rich/rev4.pdf and look at the diagram that accompanies problem #24.
 

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