A bob is whirled in a horizontal circle by means of a string at an initial speed of 10 rpm. If the tension in the string is quadrupled while keeping the radius constant, the new speed is:

Question

A body of mass 100 g is moving in a circular path of radius 2 m on a vertical plane as shown in the figure. The velocity of the body at point A is 10 m/s. The ratio of its kinetic energies at point B and C is: (Take acceleration due to gravity as 10 m/s\(^2\))

Answer 1

The centripetal force is supplied by tension (T), where \( T = mv^2/r \). When r and m are constant, T is directly proportional to \( v^2 \). If \( T_2 \) equals 4\( T_1 \), then \( v_2^2 \) equals 4\( v_1^2 \).

Given \( v_1 = 10 \) rpm, then \( v_2 = \sqrt{4 \times 10^2} = 20 \) rpm.

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A bob is whirled in a horizontal circle by means of a string at an initial speed of 10 rpm. If the tension in the string is quadrupled while keeping the radius constant, the new speed is:

The Correct Option is A

Solution and Explanation

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