There is a circular swimming pool. There is a bob at the centre of the pool at a distance of 50π m from the pool’s wall. Shyam is standing next to the
wall and holding a thread whose other end is connected to the heavy stationary bob at the centre. Holding the thread Shyam now moves along the wall for 20
seconds and the angle between the initial and final positions of the thread is 12∘. What is Shyam’s speed in metres/minute?
The distance between bob at centre and wall is nothing but radius of circular pool because radius is distance between centre of circle and boundary
(circumference). The path travelled by Shyam is along the wall of a circular boundary. So it is an arc. The angle subtended by arc is the angle between initial
and final positions of Ram which is 12∘. Hence we can find arc length by formula-
Arc length =θ360 × 2πr
Here r is radius r = 50π m
Angle subtended by arc θ = 12∘Substituting these values in the formula we get- Arc length = 103 cm
Speed = Distance/Time
Distance = Arc length = 103 cm
Time = 20 seconds = 13 minute
Speed = Distance/time = 10313 = 10 m/min