Question

Define $1J$ of work.

Answer 1

Work is defined as the product of force applied and displacement. SI unit of work is joule and CGS unit of work is erg.It is a vector quantity.

Complete step-by-step answer: Work is defined as a product of the force and displacement. For work to be done a force should act on an object and the object must be displaced. SI unit of work is joule. One joule of work is said to be when a force of one Newton displaces a body by one meter in the direction of force. $1{\text{joule = 1}}{{\text{0}}^7}{\text{erg}}$ . Dimensional formula of work is $\left[ {{\text{M}}{{\text{L}}^2}{{\text{T}}^{ - 2}}} \right]$ . Work is a scalar quantity. It can be zero, negative or positive. Its value depends on the frame of reference. SI unit of energy is also joule. Energy is defined as the internal capacity for doing work. One joule is equivalent to one watt-second. Energy like kinetic energy, potential energy, heat, electrical energy have joule as SI units.
When a hot body is placed in contact with a cold one, the former gets colder and the latter gets warmer. Certain amount of heat has passed from the hot body to the cold body. Heat is a form of energy. Heat is felt by its effect of change in degree of hotness, expansion of body, change in state and etc. SI unit of heat is joule or J. A calorie is defined as the amount of heat required to raise the temperature of a $1{\text{g}}$ water by $1^\circ {\text{C}}$ or $1{\text{K}}$ . $4.2{\text{joule}}$ is equivalent to one calorie of energy or heat.

Note: Work done is negative when the force acts opposite to the direction of displacement. Work done is positive when the force is in the direction of displacement. As any object that possesses energy can do work. So, we can say that one joule of energy is required to do one joule of work.