physics

A car travels at a constant speed of 30 mph for 20 miles, at a speed of 40 fps for the next 20 miles, and then travels the final 20 miles at 90 kph. what is the average speed of the entire trip?

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  1. d1 = V1*t1
    t1 = d1/V1 = 20/30 = 0.667 h.

    V2=40Ft/s * 1m1/5280Ft * 3600s/h = 27.3 mi/h.
    t2 = d2/V2 = 20/27.3 = 0.733 h.

    V3 = 90km/h * 1m1/1.6km = 56.3 mi/h.
    t3 = d3/V3 = 20/56.3 = 0.355 h.

    d = d1+d2+d3 = 20 + 20 + 20 = 60 mi.
    T = t1+t2+t3 = 0.667 + 0.733 + 0.355 =
    1.76 h.

    V = d/T = 60mi/1.76h = 34.1 mi/h.

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