Practice portal › Mechanical Properties of Solids › Elastic Potential Energy

A wire fixed at the upper end stretches by a length l when a force F is applied. The work done in stretching is

Asked in AIEEE 2004 · Energy stored in a stretched wire

• (1) F/(2l)
• (2) Fl
• (3) 2Fl
• (4) (Fl)/2

Step-by-step solution

Why the other options are wrong

• (1) comes from divides by the extension instead of multiplying by it, so it has the dimensions of a force gradient, not of work.
• (2) comes from treating the wire like a rigid block pulled through a distance l by a constant force; in a wire the force rises from 0 to F as it stretches, so the average force is F/2.
• (3) comes from making the opposite correction, doubling instead of halving, as if the force grew from F to 2F.

Reading this solution needs no sign-in. You only sign in to practise against the clock and keep your progress.