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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 small ball falling vertically downward with constant velocity $4m/s$ strikes elastically $a$ massive inclined cart moving with velocity $4m/s$ horizontally as shown. The velocity of the rebound of the ball is
  • A
    $4 \sqrt 2 m/s$
  • B
    $4 \sqrt 3 m/s$
  • C
    $4m/s$
  • ✓
    $4 \sqrt 5m/s$
✓

Answer

Correct option: D.
$4 \sqrt 5m/s$
d
when the ball rebounds, it experiences the same amount of momentum in the opposite direction.

Hence,

change in momentum $=2 \times \rho$

Relative velocity ( ball),

$-v$ along $x-$ axis directed to the right

$-v$ along $y$ -axis directed up

After rebound,

$V$ along $x-$ axis directed to the left

$v$ along $y-$ axis directed down

Therefore,

velocity ( rebounded ball) $=\sqrt{(} 2 v)^{2}+v^{2}$

$v \sqrt{5}$

velocity ( rebounded ball ) $=4 \sqrt{5} \mathrm{m} / \mathrm{s}$

Hence, the velocity of the rebounded ball is $4 \sqrt{5} \mathrm{m} / \mathrm{s}$

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