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5.work,energy,power and collision — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysics5.work,energy,power and collision1 Mark
MCQ
A body is dropped on ground from a height $h_1$ and after hitting the ground, it rebounds to a height $h _2$ If the ratio of velocities of the body just before and after hitting ground is $4$, then percentage loss in kinetic energy of the body is $\frac{x}{4}$. The value of $x$ is $.......$
  • A
    $374$
  • B
    $373$
  • ✓
    $375$
  • D
    $365$
✓

Answer

Correct option: C.
$375$
c
Let $V_1$ and $V_2$ are velocity just before and just after hitting the floor.

$\frac{V_1}{V_2}=4 \Rightarrow V_1=4 V_2$

$K E_{\text {bygove }}=\frac{1}{2} m V_1^2$

$K E_{\text {affor }}=\frac{1}{2} m V_2^2=\frac{1}{2} \frac{m \cdot V_1^2}{16}$

$\Delta K E=\frac{1}{2} m V_1^2\left(\frac{1}{16}-1\right)=\frac{-15}{32} m V_1^2$

$\% \text { change }=\frac{\Delta K E}{K E_{\text {before }}} \times 100 \%$

$=\frac{-15}{16} \times 100=\frac{-375}{4} \%$

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