Section C
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.
Answers
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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