Question

The large hand of a clock is $42cm$ long. How much distance does its extremity move in $20$ minutes?

• A. $88cm$
• B. $80cm$
• C. $75cm$
• D. $77cm$

Answer 1

Answer: (A)

The large hand of the clock makes a complete revolution in $60$ minutes.
$\therefore$ Angle traced out by the large hand in $20$ minutes (of time)
$=\frac{360^{\circ }\times 20}{60}=120^{\circ }=\frac{120\pi }{180}$ radian
$=\frac{2\pi }{3}$ radian
Hence, the distance moved by the extremity of the large hand $=\left(42\right)\times \frac{2\pi }{3}=88cm$. $\left(\because l=r\theta \right)$