Question 1

What is the SI unit of work?

Accepted Answer

Joule. Work is measured in joule in the SI system. Work is done when a force causes displacement along its direction. The same unit is also used for energy in mechanics.

Question 2

A force of 10 N moves an object by 5 m in the same direction. What is the work done?

Accepted Answer

50 J. Use W = F s cosθ and here θ = 0°, so cosθ = 1. So W = 10 x 5 x 1 = 50 J. Positive work increases the object’s energy in that direction.

Question 3

If the speed of a body is doubled, its kinetic energy becomes?

Accepted Answer

Four times. Kinetic energy is KE = (1/2)mv^2, so it depends on v squared. Doubling v makes v^2 four times. Therefore kinetic energy becomes four times.

Question 4

When is the work done by a force equal to zero even if the force acts?

Accepted Answer

When force is perpendicular to displacement. Work is W = F s cosθ, so it depends on the angle between force and displacement. If θ = 90°, cosθ = 0 and work becomes zero. A common example is centripetal force in uniform circular motion.

Question 5

If 600 J of work is done in 3 s, what is the power?

Accepted Answer

200 W. Power is the rate of doing work, so P = W/t. Here P = 600/3 = 200 W. Power tells how fast energy is transferred.

Work & Energy — Set 1