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# Elastic energy

When a body is stretched, work is done against the restoring force (internal force).

Elastic energy

When a body is stretched, work is done against the restoring force (internal force). This work done is stored in the body in the form of elastic energy. Consider a wire whose un-stretch length is L and area of cross section is A. Let a force produce an extension l and further assume that the elastic limit of the wire has not been exceeded and there is no loss in energy. Then, the work done by the force F is equal to the energy gained by the wire.

The work done in stretching the wire by dl, dW = F dl

The total work done in stretching the wire from 0 to l is Substituting equation (7.12) in equation (7.11), we get Since, l is the dummy variable in the integration, we can change l to lŌĆÖ (not in limits), therefore Energy per unit volume is called energy density, u = ## EXAMPLE 7.5

A wire of length 2 m with the area of cross-section 10-6m2 is used to suspend a load of 980 N. Calculate i) the stress developed in the wire ii) the strain and iii) the energy stored.

Given: Y = 12 ├Ś 1010NŌĆåmŌłÆ2.

## Solution Tags : Properties of Matter , 11th Physics : UNIT 7 : Properties of Matter
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11th Physics : UNIT 7 : Properties of Matter : Elastic energy | Properties of Matter