Question:
A car moves on a straight road for first half time with the constant speed of 20 m/sec. and the next half time with the constant speed of 60 m/sec, then calculate average speed.
Answer:
Let the points be A, B and C where the car moves from A to B with a speed of 20 m/s and from B to C with a speed of 60 m/s. Let the time taken to cover distance AB and BC be t/2 respectively as given in the problem.
We know total path length / time = average speed
For AB : Time t/2 = Distance / speed = distance / 20 Hence, distance = 20 * t/2 = 10t
For BC : Time t/2 = Distance / speed = distance / 60 Hence, distance = 60 * t/2 = 30t
Average speed = Total path length / time = (10 t + 30 t )/ t = 40 m/s
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