Question

A car travels one third of its journey along a straight road ith velocity of 15ms wo third of the remaning journey with a velocity of 25ms and the rest of the journey with velocity 20ms find its averge velocity for the entire journey

Answer 1

Let length of complete journey is x.

a/c to question,

A car travels one third of its journey along a straight road ith velocity of 15m/s

so, time taken , t1 = (x/3)/15 = (x/45)sec.....(2)

car have to travel remaining journey = x - x/3 = 2x/3

again, one third of the remaining journey with velocity 25m/s.

so, time taken, t2 = {(2x/3)/3}/25

= (2x/225)sec ......(2)

car have to travel the remaining journey = 2x/3 - 2x/9 = 2x/3 [1 - 1/3] = 4x/9

(4x/9) displacement travelled by car with velocity 20m/s.

so, time taken , t3 = (4x/9)/20 = (x/45)sec .......(3)

now average velocity of entire journey = total displacement/total time taken

= x/(x/45 + 2x/225 + x/45)

= x/(12x/225)

= 225/12

= 18.75 m/s