A Tennis ball is released from a height h and after freely falling on a wooden floor it rebounds and reaches height

(3) For uniformly accelerated/ deaccelerated motion :

$v^{2}=u^{2} \pm 2 g h$

As equation is quadratic, so, $v-h$ graph will be a parabola

Initially velocity is downwards (-ve) and then after collision it reverses its direction with lesser magnitude, i.e. velocity is upwards (+ve).

Note that time $t=0$ corresponds to the point on the graph where $h=d$.

Next time collision takes place at 3 .