Question

An athlete completes a round of a circular track of diameter 200m in 20s. Calculate a)The distance travelled by the athlete b)The magnitude of the displacement of the athlete at the end of 1minute and 10s.

Answer 1

HEY!

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a) Time taken to complete 1 rounds = 20 s

1 minute 10 seconds = 70 seconds

Number of rounds that can be completed in 70 seconds = 70/20 = 3.5 rounds

Distance travelled = circumference of circle = 2 pie r

Diameter= 200
Radius= 100

Distance travelled = 2 *3.14*100*3.5 = 2198

Displacement = Shortest distance travelled

3 rounds = Displacement = 0 , as initial and final point is same.

Now, 0.5 = half round = diameter of ground = 200 m

Thus, displacement = 200 m.

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Hope it helps...!!!

Answer 2

Length AB=200m=2R

Time taken to complete one round=20 sec
Let the starting point be A

in 70 sec or 1 min 10 sec number of rounds completed=70/20= 3.5

distance travelled=2 * 3.14 * 100  * 3.5=2198m

Displacement is change in position.
Final point - initial point.

The total rounds is 3.5 ....see in image 3 

displacement=200m

SEE THE IMAGES,
HOPE IT HELPS!!!