3.3 - Work, energy and power

Question 1

Define work done

Answer 1

The product of the magnitude of the force and distance moved by the object in the direction of the force
Unit: Joules

Question 2

Define Kinetic energy

Answer 2

The energy associated with the motion of an object with mass

Question 3

Define gravtational 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 a result of a reversible change in its shape

Question 5

State the principle of conservation of energy

Answer 5

In a closed system 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 inital 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

Thus v=√2gh

Since there is no m in the calculating the mass has no effect on the final speed - the acceleration of free fall is the same for all objects

Question 7

The rate of work done is equal to …

Answer 7

Power

Question 8

What is effiecency?

Answer 8

Efficiency (%) = (useful output power/ total input power) x 100