Question

3. An athlete completes one round of a circular track of radius 35 cm in 10 s. The displacement of the athlete at the end of 40 s is (1) 35,2 cm (2) 70 cm (3) 110 cm (4) Zero​

Answer 1

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Given parameters

The diameter of the circular track = 200 m

Radius (r) = 200/2

r = 100 m

Time is taken by an athlete to complete one round = 40 seconds.

Displacement = ??

Speed = Distance/Time

Total time athlete moves – 2 min 20 seconds

2 min 20 seconds = 2 × 60 + 20

2 min 20 seconds = 140 seconds

Need to find the distance covered in one round

Distance covered in one round = Circumference of circle

Distance covered in one round = 2πr

Distance covered in one round = 2

Distance covered in one round = 2 × 100π

Distance covered in one round =200π

Time is taken by an athlete to complete one round = 40 seconds.

Number of rounds completed in 140s = 140/40

Number of rounds completed in 140s = 35

Distance covered = 3.5 × circumference

Distance covered = 3.5 × 2πr

Distance covered = 3.5 × 2 × 3.14 × 100

Distance covered = 2200 m

Hence, the distance covered at the end of 2 min 20 seconds is 2200 m or 22 km.

And displacement is 200 m as it returns to the initial position.

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