Question

In the S.I. system, the unit of potential energy is
A. Erg
B. Dyne-cm
C. Joule
D. None of these

Answer 1

Hint: Energy spent in doing some work is equal to the work done which is equal to the product of force applied and the displacement produced in the body. The units of energy are the same as that of work done.

Complete step-by-step answer:
Energy can be of two types: Kinetic energy and potential energy. Kinetic energy is the energy possessed by a body by the virtue of its motion. Potential energy is the energy possessed by a body virtue of its position. A body at rest has zero kinetic energy but non-zero potential energy.
The unit of energy is the same as that of work as the work done by a body is equal to the energy stored in a body.
The S.I. unit of energy is joule (J) while the CGS unit of energy is erg.
The kinetic energy and potential energy are just forms of energy and share the same units as energy.
Therefore, the S.I. unit of potential is joule (J). Hence, the correct answer is option C.
Additional information:
A unit can also be expressed in terms of the quantities that it is derived from. In S.I. system, 1 joule = 1N x 1m = 1Nm
So Nm is also a S.I. unit of work and energy. Similarly, in the C.G.S. system, the unit of energy is erg and 1 erg = 1dyne x 1cm = 1 dyne-cm. So dyne-cm is also a C.G.S unit of energy along with erg.

Note: While solving numerical problems, all the quantities must be in the same system of units because the systems are not equivalent to each other but can be related through certain relations which can be used to convert from one system to another.