Question

5.
A boy completes one round of a circular track of
radius 20 m in 50 seconds. The displacement at
the end of 4 minute 10 second will be
​

Answer 1

4 minutes 10 seconds = (4*60)+10

                                    = 240+10

                                   = 250 seconds

In 50 seconds he covers = 2*(22/7)*20 m

                                         = 880/7 m

In 1 second he covers = 880/7*50

In 250 seconds he covers = 250*880/50*7

                                           = 4400/7 m

So, he moves through the circular track for = (4400/7)/(880/7)

                                                                 = 5

So, the displacement is 0, as he again comes to the same point from where he had started.

Answer 2

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Answer

Boy completes one round in 50 seconds.

This implies that his displacement is 0 when he completes one complete round.

Time given = 4 min 10 sec

= 250 seconds

No. of rounds = 250/50

= 5 rounds

Therefore, he covered a good amount of distance but his displacement is zero as he is at the point from which he started after each consecutive round(s).