Question

A car travels first half distance between two places with uniform speed of 60km/hr what should be its uniform speed for the second half of the distance so that its average speed over the entire journey becomes 90 km/hr

Answer 1

let total distance=x
so for first half , t1= x/(2*60)=x/120
and total time t=x/90

so time tken in second half= t-t1 = x/90 - x/120
=(4x-3x)/360=x/3 t2= x/(2v)=x/360
so 2v=360
v=180
Hence the speed of car should be 180 in the second half of journey to make avg velocity for the whole journey equal to 90.