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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 block is attached to a spring as shown and very-very gradually lowered so that finally  spring expands by $"d"$. If same block is attached to spring & released suddenly then maximum expansion in spring will be-
  • A
    $d$
  • ✓
    $2\,d$
  • C
    $3\,d$
  • D
    $4\,d$
✓

Answer

Correct option: B.
$2\,d$
b
In first case acceleration of block is zero always.

therefore $\mathrm{mg}=\mathrm{kx}$

$\therefore \mathrm{x}=\frac{\mathrm{mg}}{\mathrm{k}}=\mathrm{d}(\mathrm{given})$

In second case block variably accelerate from rest
to rest

$0 =-\operatorname{mg} \mathrm{x}+\frac{1}{2} \mathrm{Kx}^{2}$

$\therefore \quad \mathrm{x} =\frac{2 \mathrm{mg}}{\mathrm{K}}=2 \mathrm{d}$

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