Question

A car travels first 50 km with a constant speed of 30 km/h and next 40 km with a constant speed of 60 km/h . Calculate the average speed.

Answer 1

since equal distances are covered at 60 kmph and 40 kmph, we can apply the formula 2xy/(x+y)
Average speed= 2×40×6040+602 = 48 kmph

This formula works as follows

Let the distance to one side = x
Total distance = 2x 

Time taken for the forward journey = x60x
Time taken for the return journey = x40x
Total time = x60+x40=100x2400xx100

Average speed = Total distanceTotal Time=2x(100x2400)Total distance2100 = 48 kmph

 

Answer 2

@
average speed = distance/time
____________
as we know that time = distance/speed
____________
speed=distance/(distance/speed)
=>(50+40)km/(90/90)
=>90/1
=>90km/h=average speed
______________
SI Unit of speed is m/s
so converting in km/h in m/s
90×5/18
=>25m/s
average speed =25m/s
@:-)