Question

an athlete completes one round of a circular track of radius r in time t what is the average speed

Answer 1

40 sec needed for 1 round. 80 will be needed for 2 rounds & 120 sec for 3 rounds..we have 2 min 20 sec I.e 140 sec..now in 1 round particle comes back to its initial position. So in 1 round net displacement is 0. Also in 3 rounds that is in 120sec it will be 0..now in last 20 sec the boy will cover half the circle since he need 40 sec for 1 round...so he is now 2R displaced from initial position.

Answer 2

Distance travelled by the athlete = circumference of the circular track =
$2\pi \times r$
Time taken by him = t
Therefore average speed of the athlete = distance / time =
$\frac{2\pi \times r}{t}$
here is your answer friend..

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