Question

an an athlete completes one round of a circular track for of diameter 200 m in 40 seconds what will be the distance covered and the displacement at the end of 2 minute 20 seconds

Answer 1

Displacement will always be zero if one comes back to his original position
But incase of distance
Since, athelete takes 40sec to complete a distance of 200m
So,Athelete takes 1sec to complete a distance of 200/40
Hence,Athelete takes 160sec to complete a distance of 200/40×160=800m. (2min 40sec=160sec)
Simple Unitary method

Answer 2

Here ,

Total Time = 2 minutes 20 seconds

= 2 × 60 seconds + 20 seconds

= 120 seconds + 20 seconds

= 140 seconds.

Now , In 40 s, the number of rounds completed = 1

So , In 140 s, the numbers of rounds completed = 140 ÷ 40 = 3.5

(i) Calculation of distance covered in 3.5 rounds :-

The diameter of circular circular track is given to be 200 m , so that radius of the circular track will be half of it, which is 100 m.

Now , Distance covered in one round = Circumference of circular track

$= > 2\pi \: r$

$= > 2 \times \frac{22}{7} \times 100 \: m$

$= > 628.57 \: m$

And , Distance covered in 3.5 rounds = 628.57 × 3.5 m = 2200 m.

(ii) Calculation of displacement in 3.5 rounds :-

The athlete makes three and a half rounds of the circular track. Now , is that starts from point A , then after 3 complete rounds, he will reach at the same point. And when the athlete again starts from point a and make the remaining half round, he will reach point B which is the diametrically opposite to A. So , the displacement of athlete will be equal to the diameter of the circular tracks which is 200 m.