Question

A simple pendulum of length 25 cm and amplitude $8^o$ oscillates in a vertical plane. At t = 0, the bob is at its right extreme. At what time, the string makes an angle of $4^o$ with vertical? (Take $g=10m/s^2$ and ${\pi }^2=10$)

• A. $\frac{1}{6}$
• B. $\frac{1}{3}$
• C. 1
• D. $\frac{1}{2}$

Answer 1

The correct option is A $\frac{1}{6}$

From A to $\frac{A}{2},$ time required

$t=\frac{phase}{\omega }=\frac{\frac{\pi }{3}}{\frac{2\pi }{T}}=\frac{T}{6}=\frac{1}{6}$
$T=2\pi \sqrt{\frac{l}{g}}=2\pi \sqrt{\frac{1}{4g}}$
$T=1s$
$⟹t=\frac{1}{6}s$