A motor cyclist travels a certain distance with a uniform speed of $30\, m/s$ and immediately turns back and returns to starting point with a uniform speed $20\, m/s$. Then the average speed of the motor cycle is ..........$m/s$ :-

A person travels along a straight road for the first half time with a velocity ${v_1}$ and the next half time with a velocity ${v_2}$ . The mean velocity $V$ of the man is

A car moves a distance of $200 \;m$. It covers the first half of the distance at speed $40 \;km / h$ and the second half of distance at speed $v$. The average speed is $48\; km / h$. The value of $v$ is

If the body covers one-third distance at speed $v_1$, next one third at speed $v_2$ and last one third at speed $v_3$, then average speed will be

A train starting from rest first accelerates uniformly up to a speed of $80 \mathrm{~km} / \mathrm{h}$ for time $t$, then it moves with a constant speed for time 3t. The average speed of the train for this duration of journey will be (in $\mathrm{km} / \mathrm{h}$ ) :

A car travels a distance of $x$ with speed $v_1$ and then same distance $x$ with speed $v_2$ in the same direction. The average speed of the car is