A boy is whirling a stone around his head by means of a string The string makes

Question

A boy is whirling a stone around his head by means of a string The string makes one complete revolution every second, and the magnitude of the tension in the string is F. The boy then speeds up the stone keeping the radius of the circle unchanged, so that the string makes two complete revolutions every second What happens to the tension in the sting? The magnitude of the tension increases to four times its original value. 4F The magnitude of the tension reduces to one-fourth of its orignal value, F/4 The magnitude of the tension is unchanged. The magnitude of the tension increases to twioe its ongnal value. 2F. The magnitude of the tension reduces lo hall of its original value. F/2

Explanation / Answer

centripetal force F = mv^2/r

also as V = rW

F = mrW^2

for t = 1 , W = n*2pi/t

so when W = 2 * 2pi./t

W = 2times of Wo

so

Fnew = m r (2W0)^2

Fnew = 4 times of F

so answer is option 1

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