Question

The speed-time graph of an ascending passenger lift is given alongside.
What is the acceleration of the lift :

(i) during the first two seconds?
(ii) between second and tenth second?
(iii) during the last two seconds?

Answer 1

(i) We have to find the acceleration from the given graph.
Acceleration = slope of line AB
$$\begin{gathered} =\frac{(4.6-0)}{(2-0)}\mathrm{m}/{\mathrm{s}}^2 \\ =\boxed{2.3\mathrm{m}/{\mathrm{s}}^2} \end{gathered}$$
(ii) Between second and tenth second, it represents uniform speed, so, acceleration acting on the lift is zero.
(iii) During the last two seconds, it represents retardation of the lift, so its acceleration is (–2.3 m/s²).