A boy standing on a stationary lift (open from above) throws a ball upwards with the maximum initial speed he can, equal to $49 \mathrm{m}/\mathrm{s}$. How much time does the ball take to return to his hands? If the lift starts moving up with a uniform speed of $5 \mathrm{m}/\mathrm{s}$ and the boy again throws the ball up with the maximum speed he can, how long does the ball take to return to his hands?

On a long horizontally moving belt (Figure), a child runs to and fro with a speed $9 \mathrm{k}\mathrm{m} {\mathrm{h}}^{-1}$ (with respect to the belt) between his father and mother located $50 \mathrm{m}$ apart on the moving belt. The belt moves with a speed of $4 \mathrm{k}\mathrm{m} {\mathrm{h}}^{-1}$. For an observer on a stationary platform outside, what is the
(a) speed of the child running in the direction of motion of the belt ?
(b) speed of the child running opposite to the direction of motion of the belt ?
(c) time taken by the child in (a)and (b)?
Which of the answers alter if motion is viewed by one of the parents?

The speed-time graph of a particle moving along a fixed direction is shown in Figure. Obtain the distance traversed by the particle between 

(a) $\mathrm{t}=0 \mathrm{s}$ to $10 \mathrm{s},$ 

(b) $\mathrm{t}=2 \mathrm{s}$ to $6 \mathrm{s}$


What is the average speed of the particle over the intervals in (a) and (b)?

The velocity-time graph of a particle in one-dimensional motion is shown in Figure.

Which of the following formulae are correct for describing the motion of the particle over the time-interval ${\mathrm{t}}_2$ to ${\mathrm{t}}_1$?