Work, Energy and Power

Question 1

Define the work done by a force.

Answer 1

Work done by a force on the body is defined as the product of the force and the displacement in the direction of the force.
W = Fs cos θ

Question 2

What is the formula for elastic potential energy (EPE)?

Answer 2

EPE = ½kx^2

Question 3

State the Principle of Conservation of Energy.

Answer 3

Energy can neither be created nor destroyed, it can only be converted from one form to another.

Question 4

Derive the equation for kinetic energy KE = ½mv^2 from rest. using equations for uniformly accelerated motion in a straight line.

Answer 4

Work done = Fs
KE = mas
using v^2 = u^2 + 2as,
KE = ½m(v^2 - u^2)
= ½mv^2 (from rest, u = 0)

Question 5

Define power.

Answer 5

Power is defined as the rate at which work is done.

Question 6

Using the definition of work done by a force, derive the equation GPE = mgh, where m = mass, g = gravitational field strength, h = height from the Earth’s surface.

Answer 6

Increase in Ep = Work done by Fext against gravity to lift the body upwards
= Fext . h
= mgh (Since there is no acceleration, Fext = mg)