Consider a rubber ball freely falling from a height $h=4.9 \mathrm{~m}$ 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 the height as function of time will be

• A

  
  
  
• B

  
  
• Correct answer
  C

  
  
• D

  
  

Solution

$\mathrm{h}=\frac{1}{2} \mathrm{gt}^2, \quad \mathrm{v}=-\mathrm{gt}$ and after the collision, $\mathrm{v}=\mathrm{gt}$. (parabolic) (straight line) Collision is perfectly elastic then ball reaches to same height again and again with same velocity.

Hence, the correct answer is option: 'C'.