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JEE Main 2021 (20 Jul, Shift 1) · Spring & Elastic Energy

Spring & Elastic Energy question from JEE Main 2021 (20 Jul, Shift 1)

Q17JEE Main 2021 · 20 JUL · SHIFT 1Medium

Spring & Elastic Energy

In a spring gun having spring constant 100 N/m a small ball 'B' of mass 100 g is put in its barrel (as shown in figure) by compressing the spring through 0.05 m. There should be a box placed at a distance 'd' on the ground so that the ball falls in it. If the ball leaves the gun horizontally at a height of 2 m above the ground. The value of d is _________ m. (g = 10 m/s2).

Figure

Numerical answer type. Work it out, then open the answer.

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Answer: 1

  1. Launch speed: 12kx2=12mv2⇒v=xk/m=0.051000≈1.58\frac{1}{2}kx^2 = \frac{1}{2}mv^2 \Rightarrow v = x\sqrt{k/m} = 0.05\sqrt{1000} \approx 1.58 m/s
  2. Time to fall 2 m: t=2Hg=0.4≈0.632t = \sqrt{\frac{2H}{g}} = \sqrt{0.4} \approx 0.632 s
  3. d=vt=1.58×0.632≈1d = vt = 1.58 \times 0.632 \approx 1 m
  4. So d=1d = 1 m.
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