# Consider a rubber ball freely falling from a height $\dpi{100} h =4.9\: m$ onto a horizontal elastic plate. Assume that the duration of collision is negligible and the collision with the plate is totally elastic. Then the velocity as a function of time and the height as function of time will be Option 1) Option 2) Option 3) Option 4)

As we learnt in

If only conservative forces act on a system, total mechnical energy remains constant -

$K+U=E\left ( constant \right )$

$\Delta K+\Delta U=0$

$\Delta K=-\Delta U$

-

As the ball fall its velocity increases $v=\sqrt{2gh}=gt (in\ negative\ direction)$

as it reflect after collistion $v=v_{0}-gt.$

So velocity is linear.

Increasing while going down and decreasing while going up.

$h=h_{0} -\frac{1}{2}gt^{2}(going\ down)\ parabolic$

$h=\frac{1}{2}gt^{2}(going\ up)\ parabolic$

So correct graph is 3

Option 1)

This is an incorrect option.

Option 2)

This is an incorrect option.

Option 3)

This is the correct option.

Option 4)

This is an incorrect option.

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