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Question

A spring when compressed by 4 cm has 2 J energy stored in it. The force required to extend it by 8 cm will be

This question was previously asked in
RRB ALP 2018 CBT 2 Fitter Question Paper (21-Jan-2019) (Shift 3)
The correct answer is
200 N

Spring Physics: Energy and Force Calculation

This problem involves calculating the force required to extend a spring based on its stored energy during compression. We will use the formulas for potential energy stored in a spring and Hooke's Law.

Calculating the Spring Constant

First, we determine the spring constant (\(k\)) using the energy stored (\(E\)) when compressed by a distance (\(\Delta x_1\)).

  • Given Energy: \(E = 2\) J
  • Given Compression: \(\Delta x_1 = 4\) cm \(= 0.04\) m
  • Potential Energy Formula: \(E = \frac{1}{2} k (\Delta x_1)^2\)
  • Rearranging for \(k\): \(k = \frac{2E}{(\Delta x_1)^2}\)
  • Calculation: \(k = \frac{2 \times 2 \text{ J}}{(0.04 \text{ m})^2} = \frac{4}{0.0016} \text{ N/m} = 2500 \text{ N/m}\)

Calculating the Extension Force

Next, we calculate the force (\(F\)) needed to extend the spring by a different distance (\(\Delta x_2\)), using the calculated spring constant (\(k\)).

  • Spring Constant: \(k = 2500\) N/m
  • Given Extension: \(\Delta x_2 = 8\) cm \(= 0.08\) m
  • Force Formula (Hooke's Law): \(F = k (\Delta x_2)\)
  • Calculation: \(F = (2500 \text{ N/m}) \times (0.08 \text{ m}) = 200 \text{ N}\)

The force required to extend the spring by 8 cm is 200 N.

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