Question

a car is travelling at 54 km per hour for first 20 seconds 36 km per hour for next 30 seconds and finally 18 km per hour for 10 seconds find the average speed

Answer 1

$54kmph = 54 \times \frac{5}{18} = 3 \times 5 = 15 m/s\\ 36kmph = 36 \times \frac{5}{18} = 2 \times 5 = 10m/s \\ 18kmph = 18 \times \frac{5}{18} = 5m/s$
Total Distance travelled=15+10+5=30 m/s.
Total Time Taken=20+30+10=60 seconds.
$average \: speed = \frac{total \: distance \: travelled}{total \: time \: taken}$
$= \frac{30}{60} = \frac{1}{2} = 0.5$
So, average speed is 0.5m/s.

Answer 2

Total Distance travelled=15+10+5=30 m/s.
Total Time Taken=20+30+10=60 seconds.


So, average speed is 0.5m/s.