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5.Work, Energy, Power and Collision
normal
$A$ ball is dropped from $a$ height $h$. As it bounces off the floor, its speed is $80$ percent of what it was just before it hit the floor. The ball will then rise to $a$ height of most nearly .............. $\mathrm{h}$
A
$0.80$
B
$0.75$
C
$0.64$
D
$0.50$
Solution
$a=g$
$u=0$
$v=? ?$
$s=h$
$v^{2}-u^{2}=2 a s$
$\Rightarrow v^{2}=2 g h$
$\Rightarrow \quad v=\sqrt{2 g h}$
$u=0 \cdot 8 \sqrt{2 g h}$
$v=0$
$a=-g$
$s=? ?$
$v^{2}-u^{2}=2 a s$
$\Rightarrow e^{2}-0.64 \times 2 g h=2(-g)^{5}$
$\Rightarrow 0.64 \times 2 g h=2 g S$
$S=0.64 \mathrm{h}$
Standard 11
Physics
