A uniform thick straight wire of length pi metres is held fixed at its midpoint and then bent into the shape of a circle. By how much does its centre of mass shift?

pi m
0.5 m
2 m
pi/2 m

Correct answer: 0.5 m

Solution

The straight wire's CM is at its midpoint; after bending into a circle of circumference pi the radius is 1/2, and the CM moves to the centre of the circle, a shift equal to the radius = 0.5 m.

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