Question

27. Supriya is cycling on a circular track. She starts from point A and reaches point B in 20
minutes.
(4 marks)
a) If the speed of her bicycle is 20 km/hr, calculate the distance covered by her and her
displacement as she cycles from point A to B?
b) She cycles from point B back to point A in another 40 minutes. Calculate her average
speed and average velocity in the entire journey from point A to point B and back to
point A.
​

Answer 1

Given : Supriya is cycling on a circular track.

She starts from point A and reaches point B in 20 minutes.

Speed of her bicycle is 20 km/hr,

She cycles from point B back to point A in another 40 minutes.

To Find :  a) the distance covered by her and her displacement as she cycles from point A to B

b) average speed and average velocity in the entire journey from point A to point B and back to point A.​

Solution :

starts from point A and reaches point B in 20 minutes.

Time = 20 minutes = 20/60 hrs = 1/3  hrs

Speed of Bicycle  = 20 km/hr

Distance covered = 20 * 1/3  = 20/3  = 6.67  km

Displacement will be Diameter  = 2 × ( Radius)

π (radius)  = 20/3    ( semi circle circumference )

=> radius = 20/3π

Diameter   = 2 ×  20/3π  = 40/3π   =  4.24  km

She cycles from point B back to point A in another 40 minutes.

=> Total time = 20 + 40 = 60 minutes = 1 hr

Total Distance = 2 x 20/3  = 40/3 km

Average speed = 40/3  km/hr  = 13.33 km/hr

Return to same point hence displacement = 0  km

average velocity = 0/1 = 0    km/hr

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