Question

Natural length of a massless spring (of spring constant $k$) is $x$. It is slowly stretched by applying an external force. What is the work done in slowly stretching it from length $3x$ to $4x$?

• A. $1.5{kx}^2$
• B. $2.5{kx}^2$
• C. $3.5{kx}^2$
• D. $4.5{kx}^2$

Answer 1

The correct option is C $3.5{kx}^2$

$W=\frac{1}{2}(k{x}_1^2-k{x}_2^2)$

$W=\frac{1}{2}k(4^2-3^2)$

$W=3.5k{x}^2$