Physics Question Please Help?

M

Mark H

New member
A 150 kg merry-go-round in the shape of a uniform solid horizontal disk of radius 1.5 meters is set in motion by wrapping a rope about the rim of the disk and pulling on the rope. What constant force must be exerted on the rope to bring the merry-go-round from rest to an angular speed of .5 revolutions per second in 2 seconds.
 
You are given enough to find the angular acceleration: the final angular speed is 0.5 rev/sec, or pi radians per second. So the angular acceleration is alpha = pi/2 rad/sec^2.

Analogous to F = ma, the torque and the angular acceleration are related by T = I*alpha, where I = moment of inertia. You are told that the merry-go-round is a horizontal disk, so that should be enough to calculate I. Thus, you know the required torque.

The relationship between torque and force is T = F*r, so once you know T you can easily find F.
 
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