Question

Class 9 physics ncert

Answer 1

Answer:

Explanation:

Average speed  =  80 km/hr

Total time taken  =  T hr

Distance = 80T  km

loses 2 hrs in the first part of the journey

Distance covered = 80 (x - 2)  km  till start accelerating

Remaining hrs = T - x  hrs

accelerates at a rate of 20 km/hr till the speed reaches 100 km/h

100 = 80 + (20)T  =>  T = 1  hr

Distance covered in 1 hr  =  1 * (80 + 100)/2 = 90 km

Remaining time = T - x - 1  hr

Distance covered  =  100(T - x - 1)  km

80(x - 2) + 90 +  100(T - x - 1)  = 80T  

=> 80x - 160 + 90 + 100T - 100x - 100 = 80T

=> 20T  - 20x  = 170

=>  T  - x  = 8.5

=> x = T - 8.5

80 (x - 2)   = 80 (T - 8.5 - 2)  = 80T  - 840  km

840 km before reaching Mumbai