Question

A car travels from stop A to stop B with a speed of 30 km/hr and then returns back to A with a speed of 50 km/hr. Find : (i)displacement, (ii)distance, (iii) average velocity, (iv)average speed of the car.

Answer 1

Question 31753

I) Since displacement $\bar{S}$ is the vector which connects start and end points (which are the same), $|\bar{S}| = 0$, hence displacement is zero.

II) There is not enough information in order to find the distance between A and B. At least one more value (like, for example time in forward or reverse direction) is needed.

III) Average velocity is $|\nabla| = \frac{|\bar{S}|}{t}$. Since displacement is zero (see point I), average velocity is zero.

IV) Average speed is $v = \frac{2l}{t}$, where $l$ is the distance between A and B, and $t$ is the time spent to go forward and back. $v = \frac{2l}{\frac{l}{30} + \frac{l}{50}} = \frac{2l}{\frac{80l}{1500}} = 37.5 \, \text{km/h}$.