Question

A stone is tied to a string of length ${}^{\prime }{\ell }^{\prime }$ and is whirled in a vertical circle with the other end of the string as the center. At a certain instant of time, the stone is at its lowest position and has a speed ${}^{\prime }{u}^{\prime }$. The magnitude of the change in velocity as it reaches a position where the string is horizontal (g being acceleration due to gravity) is :

• A. $\sqrt{u^2-g\ell }$
• B. $u-\sqrt{u^2-2g\ell }$
• C. $\sqrt{2g\ell }$
• D. $\sqrt{2(u^2-g\ell )}$

Answer 1

The correct option is D $\sqrt{2(u^2-g\ell )}$