Question

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

• A. $2\pi cm$
• B. $28\pi cm$
• C. $8\pi cm$
• D. None of these

Answer 1

The correct option is B $28\pi cm$

Angle rotated in $60mm={360}^o$

$\theta =$ angle rotated in $20min\Rightarrow \frac{360}{60}\times 20\Rightarrow {120}^o$

$\theta \Rightarrow \left(\frac{2\pi }{3}\right)$

$\therefore P=r\theta =\left(42\right)\times \frac{2\pi }{3}\Rightarrow 28\pi cm$

$\therefore$ the extremity of the hand moves $28picms$.