Q. A stone of mass 1 kg is tied at one end of string of length 1 m. It is whirled in a vertical circle at constant speed of $4\ ms^{- 1}$. The tension in the string is 6 N when the stone is at $(g = 10ms^{- 2})$

A) Top of the circle
B) Bottom of the circle
C) Half way down
D) None of these
Explanation

(d) When the string makes an angle $\theta$ with the vertical, then
$T - mg\ cos\ \theta = \frac{mv^{2}}{r}$
Substituting the values, we obtain
$6 - (1)(10)\cos{\theta = \frac{1 \times (4)^{2}}{1}}$
or $6 - 10$ $cos\ \theta$=16
or $cos\ \theta = - 1 = \cos{180{^\circ}}$
$\therefore\ = 180{^\circ}$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.