Question

# A ball is thrown vertically downwards from a height of 20 m with an initial velocity $$\upsilon _0$$. It collides with the ground, loses 50 percent of its energy in collision and rebounds to the same height. The initial velocity $$\upsilon _0$$ is (Take $$g=10 \,ms^{-2}$$)

A
10ms1
B
14ms1
C
20ms1
D
28ms1

Solution

## The correct option is B $$20 ms^{-1}$$Initial  energy $$E_i = PE + KE = mgh + \dfrac{1}{2}mv^2$$Energy when it reaches the ground: $$E = \dfrac{1}{2}mv'^2$$ since PE is zero.Given, $$E = \dfrac{1}{2}E_i$$Since it rises to the  same height $$E_f =mgh +0$$ is the final energy$$\Rightarrow \dfrac{1}{2}(mgh + \dfrac{1}{2}mv^2) = E_f = mgh +0$$$$v^2 = 2gh = 2 \times 10 \times 20 = 20^2$$$$\Rightarrow v =20\:m/s$$Physics

Suggest Corrections

0

Similar questions
View More

People also searched for
View More