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Question:

A ball of mass m is tied up with string and rotated along a horizontal circle of radius r. At an instant, its velocity is v, and tension in string is T. The force required for circular motion is:

T−mv²/r

T+mv²/r

mv²/r

Zero

Solution:

Let the string make an angle θ to the normal at the point of suspension. The horizontal component of tension provides the necessary centripetal force. Therefore, Tsinθ = mv²/r.