Question

A stone tied to a string is rotated with a uniform speed in a vertical plane. If mass of the stone is $m$, the length of the string is $r$ and the linear speed of the stone is $v$, when the stone is at its lowest point, then the tension in the string will be ($g=$ acceleration due to gravity)

• A. $\frac{m{v}^2}{r}+mg$
• B. $\frac{m{v}^2}{r}-mg$
• C. $\frac{mv}{r}$
• D. $mg$

Answer 1

The correct option is A $\frac{m{v}^2}{r}+mg$


From FBD at the lowest point, as shown in the figure,
both weight $mg$ and centrifugal force $\frac{m{v}^2}{r}$ will act in the same direction.
So,
$T=mg+\frac{m{v}^2}{r}$