Question

The average speed of a car which covers half the distance with a speed of $20m/s$ and other half with a speed of $30m/s$ in equal intervals of time is

• A. $25m/s$
• B. $0m/s$
• C. $24m/s$
• D. $2.4m/s$

Answer 1

Answer: (C)

$24m/s$

Lets consider $x$ is total distance covered by the car.

The half of the distance covered with speed $20m/s$ at time $t_1$

$t_1=\frac{x}{2\times 20}=\frac{x}{40}sec$

Next half distance covered with the speed $30m/s$ at time $t_2$

$t_2=\frac{x}{2\times 30}=\frac{x}{60}sec$

Total time, $t=t_1+t_2$

$t=\frac{x}{40}+\frac{x}{60}=\frac{x}{24}$

The average speed, $v=\frac{x}{t}$

$v=\frac{x}{x/24}=24m/s$

The correct option is C.