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CBSE Class 9 Science Question 1 of 30

Motion — Question 1

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Question 1

An athlete completes one round of a circular track of diameter 200 m in 40 s. What will be the distance covered and the displacement at the end of 2 minutes 20 s?

Answer

Given,

Diameter of track (d) = 200 m

An athlete completes one round of a circular track of diameter 200 m in 40 s. What will be the distance covered and the displacement at the end of 2 minutes 20 s? NCERT Class 9 Science CBSE Solutions.

Circumference of the track = πd = 200π m

So, distance covered in 40 seconds = 200π m

Distance covered in 1 sec = 200π40\dfrac{200π}{40}

Distance covered in 2 min 20 sec (i.e., 60 + 60 + 20 = 140 sec) = 200π40\dfrac{200π}{40} x 140

= 200×22×1407×40\dfrac{200 \times 22 \times 140}{7 \times 40}

= 2200 m

Number of rounds completed in 140 sec = 14040\dfrac{140}{40} = 3.5

∴ the final position (with respect to the initial position) is at the opposite end of the circular track. So, the net displacement will be equal to the diameter of the track = 200 m.

Hence, the net distance covered by the athlete is 2200 m and the total displacement of the athlete is 200 m.