3.3 Work, energy, power

Question 1

Define work done

Answer 1

The product of the magnitude of the force and the distance moved by the object in the direction of the force. unit - Joules

Question 2

Define kinetic energy and give its unit

Answer 2

the energy associated with the motion of an object with mass. kgm^2s^-2

Question 3

define gravitational potential energy

Answer 3

the energy of an object due to its position in a gravitational field

Question 4

Define elastic potential energy

Answer 4

the energy stored by an object as a result of a reversible change in its shape

Question 5

State te principle of conservation of energy

Answer 5

In a closed sustem, energy cannot be created or destroyed but only transferred from one form to another

Question 6

if we consider a closed system where an object is moving up and down derive a formula for the velocity of an object in a gravitational field

Answer 6

All initial GPE is converted to KE as the object falls, and this KE is converted back to GPE as it rises.
Equating KE and GPE gives: mgh = 1/2mv^2
Rearranging this in terms of v^2 gives v^2 = 2gh, so v = √2gh
Since there is no ‘m’ in the calculation, the mass has no effect on the final speed - the acceleration of free fall is the same for all objects

Question 7

What is the rate of work done equal to

Answer 7

power

Question 8

what is efficiency?

Answer 8

useful power output / total input power x 100