Question

A car travels at 54 km/h for first 20s, 36km/h for next 30s and finally 18 km/h for next 10s. Find its average speed.

Answer 1

54 km/hr = 54 x 5/18 = 15 m/s
36 km/hr = 36 x 5/18 = 10 m/s
18 km/hr = 18 x 5/18 = 5 m/s

1st Case ---
Speed = 15m/s
Time = 20 s
Distance = Speed x Time = 15 x 20 = 300 m

2nd Case ---
Speed = 10 m/s
Time = 30 sec
Distance = 10 x 30 = 300 m

3rd Case ---
Speed = 5 m/s
Time = 10s
Distance = 5 x 10 = 50 m

Now Total Distance = 300 + 300 + 50 = 650 m
Total time = 20 + 30 + 10 = 60 s

Average Speed = 650/60 = 65/6 m/s

Hope This Helps You!

Answer 2

Answer:

54 km/hr = 54 x 5/18 = 15 m/s

36 km/hr = 36 x 5/18 = 10 m/s

18 km/hr = 18 x 5/18 = 5 m/s

1st Case ---

Speed = 15m/s

Time = 20 s

Distance = Speed x Time = 15 x 20 = 300 m

2nd Case ---

Speed = 10 m/s

Time = 30 sec

Distance = 10 x 30 = 300 m

3rd Case ---

Speed = 5 m/s

Time = 10s

Distance = 5 x 10 = 50 m

Total Distance = 300 + 300 + 50 = 650 m

Total time = 20 + 30 + 10 = 60 s

Average Speed = 650/60 = 65/6 m/s

Explanation: