Question

A bob is whirled in a horizontal plane by means of a string with an initial speed of ω rpm. The tension in the string is T. If speed becomes 2ω while keeping the same radius, the tension in the string becomes ______.

Options

• `T/4`

• `sqrt 2 T`

• T

• 4 T

Answer 1

A bob is whirled in a horizontal plane by means of a string with an initial speed of ω rpm. The tension in the string is T. If speed becomes 2ω while keeping the same radius, the tension in the string becomes 4 T.

Explanation:

Centripetal force (F_c) = mrω² = T    ...(i)

Now,

T' = mr(2ω)²

= 4 mrω²

= 4 T    ...[From equation (i)]