Q.

A horse rider covers half the distance with 5 m/s speed. The remaining part of the distance was travelled with speed 10 m/s for half the time and with speed 15 m/s for the other half of the time. The mean speed of the rider averaged over the whole time of motion is x/7 m/s. The value of x is ______.           [2023]


Ans.

(50)

tAB=x5 m/s

In motion BC, x=d1+d2

where d1 and d2 are the distances travelled with 10 m/s and 15 m/s respectively in equal time intervals 't'2 each.

d1=10t2,  d2=15t2

d1+d2=x=t2(10+15)=25t2

<v>=2xx5+2x25=2×255+2=507 m/s