Question

A spring of force constant 800 N$m^{-1}$ has an extension of 5 cm. The work done in extending it from 5 cm to 15 cm is

• A. 16 J
• B. 8 J
• C. 32 J
• D. 24 J

Answer 1

Answer: (B)

8 J

Answer 2

Work done, $W = \frac{1}{2}k(x_2^2 - x_1^2)$
$\, \, \, = \frac{1}{2} \times 800 [(15 \times 10^{-2})^2 - (5 \times 10^{-2})^2]$
$W = 400 \times 200 \times 10^{-4} = 8 \, J$