Its Average Speed Over this Distance is :
A car covers four successive 7 km distances at speeds of 10 km/hour, 30 km/hour, 60 km/hour respectively, Its average speed over this distance is
- 20 km/hour
- 60 km/hour
- 30 km/hour
- 40 km/hour
Answer is (1): 20 km/hour
Explanation:-
A car covers four successive 7 km distances at the speeds of 10 km/hour, 20 km/hour, 30 km/hour and 60 km/hour respectively,
Then, the total time taken by four cars to covered the distance 7 km = 7/10 + 7/20 + 7/30 + 7/60
= (7 x 6 + 7 x 3 + 7 x 2 + 7 x 1)/60
= (42 + 21 + 14 + 7)/60
= 84/60
= 7/5 hours
The total distance covered by four cars = 7 + 7 + 7 + 7
= 28 km
Then, the average speed of four cars = 28/(7/5)
= 28 x 5/7
= 4 x 5
= 20 km/hr
Hence, the answer is (1) 20 km/hr.
