Question

A car moves from position A to position B with a speed of 60 km/hr and returns with a speed of 40 km/hr. What is the average speed of the car?

Answer 1

Definition of average speed:

1. Average speed is defined as the ratio of total distance covered by a body with respect to the total time taken.
2. i.e. Average speed = total distance covered / total time taken.

Solution:

Let the speed of the car be S₁ Km/hr = 60 km/hr from A to B and S₂ Km/hr = 40 km/hr from B to A.

Let the time taken by the car from A to B be T₁ hr and T₂ from B to A.

Let the distance between A and B be x km, as shown in the figure below.

Now, total distance = x + x = 2x Km.

Also,

$$\begin{gathered} T_1=\frac{Dis\tan ce}{S_1}=\frac{x}{60} \\ {T}_2=\frac{x}{40} \\ Totaltime=T_1+T_2=\frac{x}{60}+\frac{x}{40}=\frac{40x+60x}{2400}=\frac{x}{24} \end{gathered}$$

Therefore, average speed = $\frac{2x}{{\displaystyle \frac{x}{24}}}=2x\times \frac{24}{x}=48km/hr$.