Question

A car travels from stop A to stop B with a speed of 30 m/s and then returns back to A

with a speed of 50 m/s. Find: average speed​

Answer 1

Answer:

Let the distance from A to B be x.

Then displacement of the car when it comes back to the same position is zero.

Distance travelled is 2x.

Time taken by the car when it moves from A to B is given by

t1 = Distance/Speed = x/30

Time taken by the car when it moves from B to A,

t2 = Distance/Speed = x/50

Total distance = 2x

Total time

= t1 + t2

= x/30 + x/50

= (5x + 3x)/150

= 8x/150

So, Average speed

= Total distance/Total time

= 2x/(8x/150)

= 37.5 km/hr

Answer 2

Average speed = (Total distance covered)/(Total time taken)

From A to B speed is 30 m/s and from B to A speed is 50 m/s.

Assume that the car is travels the x distance.

Time = Distance/Speed

From A to B time is x/30 hr and from B to A time is x/50 hr.

Average speed = (x + x)/(x/30 + x/50)

= 2x/(8x/150)

= 2x*150/8x

= 37.5 m/s

Hence, the average speed of the car is 37.5 m/s.