The stiffness of a spring is 20 N/cm. Calculate the work done to stretch the spring by 7 cm.

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  1. 1.40 joules
  2. 140 joules
  3. 4.90 joules
  4. 2.50 joules

Answer (Detailed Solution Below)

Option 3 : 4.90 joules
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Concept:

The work done by the spring is calculated by:

\(W=\frac {1}{2} KX^2\)

where W = work done in Joules

K = stiffness in N/cm

X = displacement in cm

Calculation:

Given:

K = 20 N/cm

X = 7 cm

Work done = \(\frac {1}{2} \times 20 \times7^2 = 490\)N cm = 4.9 joule

So work done is 4.9 joule.

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