An athlete complete one round of a circular track of diameter 40 m in 12 sec. What will be the distance covered and displacement at the end of 42 sec

The person takes 12 seconds to complete 1 round.

42 = 12 + 12 + 12 + 6

So at the end of 42 seconds he will have completed 3 full and 1 half circle.

So he will be at the point diametrically opposite to the point from where he started at t = 0.

 

So, displacement = 2R = D = 40m

 

Now, R=20m

Distance = 3 Full circles + 1 half circle

= 3x2x?xR + ?xR = 7x?xR = 22x20 = 440m is the distance.