Module 3.3 - Work, Energy and Power ✓

Question 1

What is ‘work’?

Answer 1

‘Work’ is the amount of energy transferred between stores when a force causes a movement of some sort

Question 2

State the law of conservation of energy

Answer 2

conservation of energy - Energy can’t be created or destroyed, only transferred from one store to another. The total energy in a closed system will not change.

Question 3

What are the 7 energy stores?

Answer 3

Chemical, gravity, kinetic, thermal, elastic, nuclear, electric-magnetic

Question 4

What is the equation for work done?

Answer 4

W = Fx

work done = force * distance moved

Question 5

Define the joule

Answer 5

One Joule is the work done when a force of 1N moves an object through a distance of 1 metre

Question 6

Define power

Answer 6

Power is the rate of doing work (rate of energy transfer)

Question 7

What is the defining equation for the watt, and what is it’s definition?

Answer 7

P = W*t

1 watt is a rate of energy transfer equal to 1 joule per second (Js^-1)

Question 8

Derive the equation P = F*v

power = force * velocity

Answer 8

1) P = W/t
2) also, W = Fx
3) > P = Fx/t
4) But v = x/t so P = Fv

Question 9

Oh yeah btw deriving a force (Fcos(*)) also works for velocity so that’s useful for P=Fv

Answer 9

ok ye nice

Question 10

How do you derive the equation for kinetic energy?

Answer 10

1) The change in kinetic energy is equal to the work done so KE = Fx
2) Using F = ma, KE = max
3) Using a = (v-u)/t and t = ((u+v)/2)*t, KE = 1/2mv^2 - 1/2mu^2 (after simplifying)
4) The kinetic energy of an object is the kinetic energy of that object compared to when it is at rest so u=0:
KE = 1/2mv^2

Question 11

What is Gravitational Potential Energy?

Answer 11

GPE - The energy an object has due to it’s position in a gravitational field

Question 12

How do you derive the equation for Gravitational Potential Energy?

Answer 12

1) The GPE gained is equal to the work done moving an object upwards height h, so GPE = W = F*h
2) The force that this work is done against is the force of gravity, which is equal to the weight of the object mg. So GPE = mgh

Question 13

What is efficiency?

Answer 13

Efficiency is a measure of how well a device converts input energy to desired output energy

Question 14

What is the equation for efficiency?

Answer 14

Efficiency = useful output energy/total input energy * 100%

Question 15

Give an example of how energy in the nuclear store can be increased/decreased?

Answer 15

Increase - Making very high mass nuclei
Decrease - High mass nuclei splitting apart
- Low mass nuclei joining together

Question 16

How would you increase the potential energy stored by a system of magnets or charges?

Answer 16

Move the charges/magnets further apart to increase the electric-magnetic energy (just like GPE increases with a greater height)