JEE MAIN - Physics (2023 - 25th January Evening Shift - No. 26)
A body of mass 1 kg collides head on elastically with a stationary body of mass 3 kg. After collision, the smaller body reverses its direction of motion and moves with a speed of 2 m/s. The initial speed of the smaller body before collision is ___________ ms$$^{-1}$$.
Answer
4
Explanation
Before collision
_25th_January_Evening_Shift_en_26_1.png)
After collision
_25th_January_Evening_Shift_en_26_2.png)
Momentum conservation
u + 0 = 3 v – 2
3v - u = 2 …(1)
$$ \begin{aligned} & \frac{v+2}{u}=1 \Rightarrow v+2=u \\\\ & u-v=2 \quad ....(2) \end{aligned} $$
Adding (1) and (2)
$$ \begin{aligned} & 2 v=4 \\\\ & v=2 \mathrm{~m} / \mathrm{s} \\\\ & \therefore u=4 \mathrm{~m} / \mathrm{s} \end{aligned} $$
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