A person goes from point $P$ to point $Q$ covering $1 / 3$ of the distance with speed $10 \,km / h$, the next $1 / 3$ of the distance at $20 \,km / h$ and the last $1 / 3$ of the distance at $60 \,km / h$. The average speed of the person is ............ $km / h$
$30$
$24$
$18$
$12$
Position-time graph for a particle is shown in figure. Starting from $t=0$, at what time $t$ is ......... $s$, the average velocity is zero
A car starts from rest and moves with uniform acceleration $'a'$ on a straight road from time $t = 0$ to $t = T$ . After that, a constant deceleration $'a'$ brings it to rest. In this process the average speed of the car is
A car moves for half of its time at $80\, km/h$ and for rest half of time at $40\, km/h$. Total distance covered is $60 \,km$. What is the average speed of the car.........$km/h$
A $150 \,m$ long train is moving with a uniform velocity of $45 \,km/h$. The time taken by the train to cross a bridge of length $850 $ meters is..........$sec$
A car travels from $A$ to $ B $ at a speed of $20\,\,km/hr$ and returns at a speed of $30\,\,km/hr$. The average speed of the car for the whole journey is............$km/hr$