Question

When a metal wire elongates by hanging a load on it, the gravitational potential energy is decreased.
(a) This energy completely appears as the increased kinetic energy of the block.
(b) This energy completely appears as the increased elastic potential energy of the wire
(c) This energy completely appears as heat.
(d) None of these.

Answer 1

When a metal wire elongates by hanging a load on it, the potential energy is transformed a little into kinetic energy. Thus, none of these option.

• The reduced gravitational potential energy transforms in part as elastic energy, as kinetic energy and also in the form of dissipated heat energy.
• The gravitational potential energy decreased when a mass is hanged by a wire is mgl (where l is the elongation) of the wire.
• In a wire, the elastic potential energy increased as 1⁄2mgl. Therefore the decreased gravitational energy potential will never fully appear as increased kinetic energy or increased elastic potential energy or heat.

Answer 2

When a metal wire elongates by hanging a load on it, the gravitational potential energy is decreased. Then Option (d) None of these is the correct answer.

Explanation:

• In a wire, when a mass is hanged, there will be a decrease in the gravitational potential energy, which is mgl, where ‘l’ is the elongation. But there can be seen an increase in the elastic potential energy, which is denoted as ½ mgl.
• Therefore, the reduction in the gravitational potential energy will not appear completely as increased elastic potential energy or increased kinetic energy or as heat.