Rotational Motion - Self Test

Solution to Question 2: Definition of Torque

Recall that torque, , is the cross product of the moment arm, r, and the force applied, F. In other words
Since the pivot point (the point about which the object rotates) is at the centre of the merry-go-round, then the moment arm vector, r, points from the centre to the rim of the merry-go-round. Using the Right Hand Rule, we find that the torque points into the screen. 

Be careful with the moment arm vector. It is not the diameter of the merry-go-round, which was the given quantity, but the radius. So

    r = d/2 = 1.5 m
Also, note that the angle between the two vectors, placed tail-to-tail, would still be  = 110. Substituting for r, F, and , we get
    = (1.5) (50) sin(110)
    = 70 N (into the screen)

Figure 1 Diagram from Question 2


Explanation of Torque
Example Problem on Torque
Continue to: Question 3: Net Torque
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