physics - work,power,efficiency

Question 1

How is work done?

Answer 1

Work is done when a force is applied and an object is moved a distance. This transfers energy.

Question 2

How do we calculate work done?

Answer 2

Work done = force × distance

• Work (Joules, J), Force (Newtons, N), Distance (metres, m)

Question 3

How would we define a joule?

Answer 3

1 Joule is the energy transferred when a force of 1 N causes a displacement of 1 m

Question 4

What properties does a moving object have?

Answer 4

A moving object has mass and velocity (speed in a direction)

Question 5

What is the kinetic energy store of an object?

Answer 5

The kinetic store of an object relates to its motion. The faster an object moves, the more energy it has in its kinetic store.
A moving object also has mass and if a larger mass travels at the same speed it would have more energy in its kinetic store.

Question 6

How would we calculate the amount of energy in the kinetic store of an object?

Answer 6

Kinetic energy = 1/2× mass × velocity2
-Kinetic Energy (Joules, J), Mass (kilograms, kg), Velocity (metres per second, m/s)

Question 7

What is the elastic potential energy store of
an object?

Answer 7

elastic potential store of an object relates to how stretched it is. The more stretched (extended) it is, the more energy it has in its elastic store.

Question 8

How would we calculate the amount of energy in the elastic potential store of an object?

Answer 8

Elastic potential energy = 1/2 × spring constant × extension2

-Elastic Potential Energy (Joules, J), Spring Constant (Newtons per metre, N/m), Extension (metres,
m)

Question 9

What is the gravitational potential energy
store of an object?

Answer 9

gravitational potential store of an object relates to how high above the Earth’s surface it is. The higher it is, the more energy it has in its gravitational potential store.

Question 10

How would we calculate the amount of energy in the gravitational potential store of
an object?

Answer 10

Gravitational potential energy = mass × gravitational field strength × height

Question 11

How would we calculate the power of an energy transfer?

Answer 11

Power =workdone/time

Question 12

What is the value of the gravitational field strength on the Earth and the Moon?

Answer 12

Earth: g = 9.8 N/kg
Moon: g = 1.6 N/kg

Question 13

What is power?

Answer 13

Power is the rate of transferring energy, also considered as the rate of doing work.

Question 14

How would we define a Watt?

Answer 14

1 Watt is equal to a transfer of 1 joule per second.

Question 15

What does it mean if a kettle has a 3 kW rating?

Answer 15

This kettle transfers 3000 J of energy to the thermal store of the water in it per second.
This kettle does 3000 J of work to the water in it every second.

Question 16

What is the law of conservation of energy?
How do we apply this law?

Answer 16

Energy cannot be created or destroyed, only stored and transferred.

The total energy output from a device is equal to the total energy input.

Question 17

What do we mean for a device to be efficient?

Answer 17

If a device is efficient it transfers its energy usefully.

Question 18

If a device is inefficient what does it do?

Answer 18

If a device is inefficient it loses energy to the surroundings (usually by heating), we call this energy dissipated or wasted,

Question 19

How do we calculate the efficiency of an
energy transfer?

Answer 19

Efficiency (%) = useful/total ×100