A 8kg stone tied at the end of a string 1 metre long is whirled in a vertical circle. At the instant when the string makes an angle theta with the vertical, the speed of the stone is `4ms^(-1)` and the tension in the thread is 104N. Then theta is.

Options

A. `0^(@)`
B. `30^(@)`
C. `60^(@)`
D. None of these

Answer

C

Explanation

`T-mgcostheta=(mv^(2))/(r)`
or `104-8xx10costheta=(8xx4xx4)/(2)`
or `104-8costheta=64`
or `80costheta=104-64`
or `costheta=(40)/(80)=(1)/(2)`
:. `theta=60^(@)` .