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A person walks first at a constant speed of 4.90 m/s along a straight line from point A to point B and then back along the line from B to A at a constant speed of 2.70 m/s.
(a) What is her average speed over the entire trip?

  • physics - ,

    It is not the average of 4.9 and 2.7, because she spends more time walking at the slower speed.

    Let the total distance between A and B be D

    t1 = D/4.9 t2 = D/2.7

    Average speed = 2D/*t1 + t2)
    = 2D/[(D/4.9) + (D/2.7)]
    = 2/[(1/4.9) + 1/(2.7)] = 3.38 m/s

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