Question

A stone tied to a string of length \(L\) is whirled in a vertical circle with the other end of the string at the centre. At a certain instant of time, the stone is at its lowest position and has a speed \(u\). The magnitude of change in its velocity, as it reaches a position where the string is horizontal, is \(\sqrt{x(u^2−gL)}\). The value of \(x\) is

• A. 3
• B. 2
• C. 1
• D. 5

Answer 1

The Correct Option is B

\(\overrightarrow v=\sqrt{u^2−2gL\hat j}\)

\(\overrightarrow u→=u\hat i\)

\(∴|\overrightarrow v−\overrightarrow u|=\sqrt{(u^2−2gl)+u^2}\)

=\(\sqrt{2u^2−2gl}\)

\(∴ x = 2\)