A ball thrown up from a location, returns back at the same location. Which of the following statements are correct.

$(a)$ Distance travelled by ball can be zero
$(b)$ Displacement of ball is zero
$(c)$ Average velocity of ball is zero
$(d)$ Acceleration of the ball is zero

During the first $18\,min$ of a $60\,min$ trip, a car has an average speed of $11\,m / s$. What should be the average speed for remaining $42\,min$ so that car is having an average speed of $21\,m / s$ for the entire trip?

A car runs at a constant speed on a circular track of radius $100\,m$ , taking $62.8\,sec$ for every circular lap. The average velocity and average speed for each circular lap respectively is 

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 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 the first half of a distance between two places at a speed of $30\, km/hr$ and the second half of the distance at $50 \,km/hr$. The average speed of the car for the whole journey is..........$km/hr$