Question

A 2 kg stone at the end of a string 1 m long is whirled in a vertical circle at a constant speed. The speed of the stone is 4 m/sec. The tension in the string will be 52 N, when the stone is

• A. At the top of the circle
• B. At the bottom of the circle
• C. the string is horizontal
• D. the string makes an angle of 45 to the vertical

Answer 1

The correct option is

A

At the bottom of the circle

When stone is at the bottom position

Three force will act on it

Tension of the string in upward direction and weight and centrifugal force in downward direction

We can write as

Weight = mg = 20N

Centrifugal force = $\frac{m{v}^2}{r}$ = $\frac{2\times (4{)}^2}{1}$ = 32N

These two forces will be balanced by tension

So,

$T_{Bottom}$ = mg+$\frac{m{v}^2}{r}$

Hence, tension in the string at the bottom place will be 52 N