When a ball is dropped on a floor then

$y=\frac{1}{2}\mathrm{ }\mathrm{g}{t}^2 \dots \left(\mathrm{i}\right)$

So, the graph between $y\mathrm{a}\mathrm{n}\mathrm{d}\mathrm{ }t$ is a parabola. Here $y$ decrease as time decrease. When the ball is bounces back then

$y=ut-\frac{1}{2}\mathrm{g}{t}^2 \dots \left(\mathrm{i}\mathrm{i}\right)$

Eq. (ii) is also the form of a general equation of parabola so the graph between $y \mathrm{a}\mathrm{n}\mathrm{d}\mathrm{ }t$ will be a parabola. Here $y$ increases when the time increases. Hence, the required graph between $y \mathrm{a}\mathrm{n}\mathrm{d}\mathrm{ }\mathrm{t }$is shown in the figure.