Question

A car travels 1/3 of the distance on a straight road with a velocity of 10 km/h, next one-third with a velocity of 20 km/h and the last one-third with a velocity of 60 km/h. Then the average velocity ofthe car (in km/h) during the whole journey is

• A. 30
• B. 20
• C. 18
• D. 15

Answer 1

Answer: (C)

18

let distance to be covered is 1800.

then time taken for first 1/3 is $T_1=\frac{600}{10}=60sec$

time taken for second 1/3 is $T_1=\frac{600}{20}=30sec$

time taken for third 1/3 is $T_1=\frac{600}{60}=10sec$

total time taken is 100 sec.

av velocity is $\frac{1800}{100}=18km/s$.