(a) distance between delhi and agra is 200km. atrain travels thefirst 100km at the speed of 50km/h. how fast must the train travel next 100 km so as to average 70km/h for the whole joueney?
(b) ona 120 km track, a train travel the first 30 km at speed of 30 km/h how fast must the train travel the next 90km so as to average 60km/h for the entire tip?

Asked by ahujarajesh11 | 14th Jun, 2015, 03:22: PM

Expert Answer:

Time taken to travel first half distance = 100/ 50 = 2 hrs
 
Time taken to travel second half distance = 100/v
 
Average speed = 200/ (2 + 100/v)
70 = 200/ (2 + 100/v)
 
2 + 100/v = 20/7
100/v = 20/7 - 2 = 6/7
v = 100 * 7/6 Km/h
 v = 700/6 km/h 
 
NOTE: Kindly ask the other query as a separate query

Answered by Yashvanti Jain | 15th Dec, 2017, 11:47: AM