What is the torque if the rope is attached

[chaotiiic]

Homework Statement

a large stone obelisk that is 8meters tall is laid down flat in the center of a Roman piazza and is going to be tilted into place by a rope and pulley system tied to a team of donkeys. If the team of donkeys always pulls with a constant force of 4500N, what is the torque if:
a) the rope is attached to the middle of the obelisk
b) the rope is attached to the end of the obelisk at a 45 degree angle?
c) the rope is attached perpendicularly to the end of the obelisk?

Homework Equations

t = F * I

The Attempt at a Solution

a) 4m * 4500 = 18,000N*m
b) (8m)(cos45)(4500N) = 25455N*m
c) is it zero?

 

[BruceW]

hmm. The question doesn't say what point the torque is meant to be calculated around. But I think you have chosen the correct point (the pivot point), this seems the most obvious choice.

I think you've got questions a) and b) right (But be careful with the rounding in part b, it looks like you have rounded down when it should have been rounded up). For question c, think of how the rope was attached in question a.

 

[chaotiiic]

a and b are right. c is 8*4500=36,000

 

[BruceW]

That sounds right to me. (I'm guessing you have had your work marked already?) Do you get why the answer to c is what it is?

 

[asteriatic]

Yes, the torque would be zero in this case because the force is acting perpendicular to the obelisk and would not cause it to rotate.