Topic 1: Energy

Question 1

What is the specific heat capacity of a substance?

Answer 1

The amount of energy needed to raise the temperature 1 kilogram of substance by 1 degree.

Question 2

What are the units of specific heat capacity?

Answer 2

J/°C/kg

Question 3

What is the definition of power?

Answer 3

The rate at which energy is transferred (or rate at which work is done).

Question 4

What is a powerful machiene?

Answer 4

A powerful machined is not one that can exert a strong force but one that can transfer lots of energy is a short space of time.

Question 5

What is the equation for kinetic energy?

Answer 5

KE = ½ x Mass x (Velocity)²

Question 6

What is kinetic energy?

Answer 6

The energy that is stored when something moves depending on its velocity and mass.

Question 7

What is the equation for elastic potential energy?

Answer 7

EPE = ½ x Spring Constant x (Extension)²

Question 8

What is elastic potential energy?

Answer 8

It is the energy stored when you stretch or squash an object as long as limit of proportionality

Question 9

What is the equation for gravity potential energy?

Answer 9

GPE = Mass x Gravitational Field Strength x Height

Question 10

What is gravitational potential energy?

Answer 10

It is the energy that is stored in an object when its lifted in a gravitational field depending on its height and mass.

Question 11

What are the two equations for power?

Answer 11

power = energy transferred/time
power = work done/time

Question 12

What is the unit of power?

Answer 12

Watt (W)

Question 13

Two motors lift the same mass through the same
height. Motor A does this in half the time of Motor B.
Which dissipates the most power?

Answer 13

Motor A as the energy transferred is the same but
the time taken is less (P=E/t).

Question 14

What are the energy changes involved when a ball is thrown upwards and then returns to its starting position?

Answer 14

Upwards: KE is converted to GPE. Peak: Maximum GPE, zero KE. Downwards: GPE is converted to KE.

Question 15

What are the energy transfers for a bungee jumper?

Answer 15

When falling, the GPE is converted to KE of jumper. As the cord tightens, KE is converted and stored as Elastic Potential Energy (EPE). At lowest point, the jumper’s initial GPE equals the EPE stored in the cord.

Question 16

Why does a bungee jumper slows down once the
cord begins to stretch?

Answer 16

Kinetic energy decreases since it is converted to elastic potential energy. Since KE is proportional to (velocity)²,
as KE decreases, so does velocity.

Question 17

What are examples of chemical energy stores?

Answer 17

Food, fuel (eg. wood, coal, petrol), batteries.

Question 18

What are the eight different energy stores?

Answer 18

Kinetic, gravitational potential, elastic potential, chemical, magnetic, nuclear, thermal, electrostatic

Question 19

What are the four ways energy can be transferred?

Answer 19

Mechanically, electrically, heating and radiation.

Question 20

What are happens to the energy in a system when it changes?

Answer 20

The energy is transferred into or away from the system, between the objects in the system or between different types of energy stores.

Question 21

What is the conservation of mass?

Answer 21

Energy cannot be created or destroyed it can only be transferred into different forms or dissipated.

Question 22

What is waste energy?

Answer 22

Energy that is not used by the device for its desired purpose.

Question 23

What is dissapated energy?

Answer 23

This is another name for “waste energy”.

Question 24

What is form is waste energy normally lost in?

Answer 24

Heat, light or frictional forces.

Question 25

Are there are changes to the total energy of a ball that is kicked, assuming no external forces act on it?

Answer 25

The total energy of a system remains the same due to the conservation of energy law.

Question 26

What are the energy changes that occur in a filament light-bulb when it is turned on?

Answer 26

Electrical energy is transferred into light and heat energy. The light energy is useful whereas the heat energy is waste energy.

Question 27

What is the equation for efficiency?

Answer 27

efficiency = useful output energy/total energy input

Question 28

What is a useful device?

Answer 28

A device that can transfer energy from one store to another with the least amount of wasted energy.

Question 29

Is any device 100% useful?

Answer 29

No except electric heaters as if they lose energy as heat is still useful.

Question 30

How might something that is moving not fully be efficient?

Answer 30

Because there will be at least one frictional force be acting against it causing energy to be dissipated.

Question 31

What are three ways that energy transfer can be reduced?

Answer 31

Through lubricants, streamline and insulation.

Question 32

How does streamline reduce energy transfer?

Answer 32

It creates less drag, air resistance and friction as air can more easily flow over.

Question 33

How does lubricants reduce energy transfer?

Answer 33

They reduce friction and are usually liquids such as oil so they can flow easily on objects.

Question 34

How does insulation reduce energy transfer?

Answer 34

It prevents energy loss as having it makes the walls have low thermal conductivity which will slow the energy loss.

Question 35

What are some types of insulation?

Answer 35

Cavity wall insulation, loft insulation, double glazed windows and draught excluders

Question 36

What are cavity walls and cavity wall insulation?

Answer 36

A cavity wall is an air gap between inner wall and outer wall in house which reduces energy transferred by convection through the walls. Cavity wall insulation is when the gap is filled with foam.

Question 37

What is loft insulation?

Answer 37

Insulation that reduces convection currents that are created in the loft

Question 38

What are double glazed windows?

Answer 38

They have an air gap between two sheets of glass which prevents energy transfer by convention through the windows.

Question 39

What are draught excluders?

Answer 39

A strip of material around doors and windows that reduce energy transfer by convection.

Question 40

What is conduction?

Answer 40

Conduction is the process where vibrating particles transfer energy to neighbouring particles.

Question 41

What is the process of conduction?

Answer 41

The particles in the part of the object being heated vibrate and collide with each other these collisions cause energy to be transferred between particles kinetic energy stores, once energy is transferred through the whole object it transfers to the surroundings or anything touching.