Question

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:

• A. 20 rpm
• B. 40 rpm
• C. 5 rpm
• D. 10 rpm

Answer 1

The Correct Option is A

Tension (T) provides the centripetal force: T = mv²/r. With r and m constant, T ∝ v². If

T₂ = 4T₁, then v₂² = 4v₁².

Given v₁ = 10 rpm, then v₂ = √4 × 10² = 20 rpm.