during practice an athlete runs in a straight line from point X to point Y and then back along the same path from Y to X .If she runs at a constant speed of 3m/s from X to Y and then at a constant speed of 6m/s from Y to X , what is her average speed for the entire run?

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Solution

Dear student,

Let the distance between X and Y be 'd=90' meters.

Then, the time taken for the athlete from X to reach Y while running at 3m/s will be , 90/3 = 30 s
Similarly, the time taken for her from Y to reach X while running at 6 m/s will be, 90/6 = 15s

The total distance covered by the athlete will be 2d = 2 $\times$ 90 = 180 m.
Also total time taken = 30 +15 =45 s

Then average speed for the entire run = Total Distance/Total Time = 180/45 = 4 s

The result will be the same for any positive value of d.

Regards

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