Question

a woman drives at a speed of 20m/s for part of a trip and at a speed of 30m/s for the rest of the trip if she spends 10 minutes driving at each speed determine her average speed for the full trip. If instead she drives 10 kilometers at each speed determine her average speed for the full trip.

Answer 1

10 min = 600 s

600 s (20 m/s + 30 m/s) = 30 km

ave spd = 30 km / 20 min = 1.5 km/min


10 km / 20 m/s = 500 s

10 km / 30 m/s = 1000/3 s

20 km / (1500/3 s + 1000/3 s) =
... 60 / 2500 km/s = 36/25 km/min =
... 1.44 km/min

Answer 2

a. (20+30)/2 = 25 m/s. = Avg. speed.

b. 20*t1 = 10,000m., t1 = 500 s.

30*t2 = 10,000m, t2 = 333.3 s.

Total time = t1+t2 = 500 + 333.3 = 833.3 s.

Avg. speed = (d1+d2)/(t1+t2) = 20,000/833.3 = 24 m/s.

Answer 3

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