Q134 / 150 · MHT CET 2018 · Physics

A mass attached to one end of a string crosses topmost point on a vertical circle with critical speed. Its centripetal acceleration when string becomes horizontal will be ( $g =$ gravitational acceleration)

A
$g$
Correct answer
B
3 $g$
C
4 $g$
D
6 $g$

Solution

Critical velocity at top most point

v = \sqrt{r g}

∴

Velocity when string become horizontal

v' = \sqrt{υ^{2} + 2 g r}

= \sqrt{3 g r}

Centripetal acceleration

= \frac{υ^{2}}{r} = \frac{3 r g}{r} = 3 g

Hence, the correct answer is option: 'B'.

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