Question 1

When is work said to be done in physics?

Accepted Answer

Work is done only when a force acts on an object and the object is displaced in the direction of the force. Mathematically, $W = F 	imes s$. If displacement is zero, work done is zero.

Question 2

What is the SI unit of work?

Accepted Answer

The SI unit of work is Joule (J), which is equivalent to Newton-meter ($N\cdot m$) or $kg \cdot m^2/s^2$.

Question 3

Which of the following is an example of negative work done?

Accepted Answer

Negative work is done when the force and displacement are in opposite directions (angle is $180^\circ$). Frictional force acting on a moving object is a classic example of negative work.

Question 4

What is the kinetic energy of an object of mass 'm' moving with a velocity 'v'?

Accepted Answer

The kinetic energy (KE) possessed by an object due to its motion is given by the formula $Ek = \frac{1}{2}mv^2$.

Question 5

What is the potential energy of an object of mass 'm' at a height 'h' above the ground?

Accepted Answer

Gravitational potential energy (PE) is the energy stored in an object due to its position or height above the ground, given by $Ep = mgh$.

Work and Energy — CBSE Class 9 Science Important Questions & Revision Notes