Answer:
39 km/h
Explanation:
Velocity is the rate of change of distance in a given direction with time. Mathematically,
Velocity = Displacement/time
Like speed, velocity is measured in Km/h or m/s.
Given that the car travels at 54 km/h for first 20seconds,
since 60 seconds = 1 minute and
60 minutes = 1 h,
20 seconds
= 20/(60 ×60) h
= 1/180 h
In the same vein,
30 seconds
= 30 / (60 ×60) h
= 1/120 h
10 seconds
= 10/(60 ×60) h
= 1/360 h
Hence if the car travels 54 km/h for 10 seconds, the distance covered
= 54 × 1/180
= 3/10 Km
If the car travels 36km/h for next 30seconds, the distance covered
= 36 × 1/120
= 3/10 Km
If the car travels 18km/h for next 10 seconds, the distance covered
= 18 × 1/360
= 1/20 km
Total distance = 3/10 Km + 3/10 Km + 1/20 Km
= 13/20 Km
Total time spent = 20 + 30 + 10
= 60 seconds
= 1/60 h
Average velocity = 13/20 km/ 1/60 h
= 39 Km/h