3.3 Work, energy and power

Question 1

What is the equation for work?

Answer 1

Work= force applied x distance moved in the direction of the force

W= Fd

Question 2

What sort of quantity is work?

Answer 2

Scalar because it has magnitude but not direction.

Question 3

Define work done.

Answer 3

The work done, or energy transferred is the product of the force and the distance moved by the direction of movement.

Question 4

What is the unit for work?

Answer 4

Joule (J)/ Newton metre (Nm)

Question 5

When is one joule of work done?

Answer 5

One joule of work is transferred when a force of 1 newton causes an object to move a distance of 1 metre in the direction of the force.

Question 6

A body has a resultant force acting in a certain direction, causing the body to accelerated. What is the size of the force in the direction perpendicular to the direction of motion?

Answer 6

The force does no work in a direction perpendicular to the direction of motion.

Question 7

What is the principle of conservation of energy?

Answer 7

The principle of conservation of energy states that the total energy of a closed system remains constant. Energy can neither be created or destroyed, it can only be transferred from one source to another.

Question 8

What is a closed system?

Answer 8

A closed system is any system in which all the energy transfers are accounted for. Energy or matter cannot enter or leave a closed system.

Question 9

What does it mean if a light bulb is 3% effcient?

Answer 9

97% of the energy from the light bulb is wasted while only 3% of energy transferred is transferred usefully to light energy.

Question 10

What is an objects gravitational potential energy?

Answer 10

The energy an object has because of it’s position.

Question 11

What factors effects gravitational potential energy?

Answer 11

• Vertical high (m)
• Mass (kg)
• Value of gravitational energy (N Kg^-1)

Question 12

What is the relationship between work done and energy transffered?

Answer 12

work done = energy transferred

Question 13

What is the equation for gravitation potential energy?

Answer 13

E = mgh

Question 14

What is the equation for kinetic energy?

Answer 14

Ke = 0.5 x m x v²

Question 15

What is the relationship between kinetic energy and gravitational potential energy?

Answer 15

loss in potential energy = gain in kinetic energy

mgh = ½mv²

This is an example of the principle of conservation of energy.

Question 16

What will happen to the kinetic energy of an object if all factors are kept the same, but its velocity is doubled?

Answer 16

When you work out kinetic energy, the velocity is squared. This means if the velocity is doubled, the kinetic energy will increase by a factor of 4.

Question 17

Define power?

Answer 17

Power is defined as the rate of doing work.

It is the rate at which energy is transferred from one form to another.

Question 18

What is the unit for power?

Answer 18

Watts (W)

Question 19

What does it mean is a bulb has a rating of 60W?

Answer 19

It means that it transfers 60J of electrical energy to other forms of energy of every second it is turned on.

Question 20

What is the equation for power in terms of time and energy?

Answer 20

Power= work done/ time taken

Question 21

What is the equation for power including force?

Answer 21

Power = force x velocity

Question 22

What is the equation for efficiency?

Answer 22

Efficiency= (useful output energy/ total input energy) x100

Question 23

Why do we need to work out the efficiency of a devise?

Answer 23

Transfers can never be 100% efficient, energy is always transferred or other forms, which are not useful.

Question 24

What is a sankey diagram?

Answer 24

Sankey diagrams are usually used to represent to represent power production and energy problems.

Question 25

What are the forms energy can come in?

Answer 25

• Kinetic
• Gravitational potential
• Thermal
• Elastic potential
• Nuclear

Question 26

What machines show the transfer of chemical to heat energy?

Answer 26

Oil burner/ matches

Question 27

What machines show the transfer of electrical to sound energy?

Answer 27

Radio

Question 28

What machines show the transfer of chemical to sound and light energy?

Answer 28

Battery operated appliance

Question 29

What machines show the transfer of nuclear to electrical energy?

Answer 29

Nuclear power station

Question 30

What machines show the transfer of gravitational potential to kinetic energy?

Answer 30

Roller-coaster/ swing/ pendulum

Question 31

What machines show the transfer of kinetic to electrical energy?

Answer 31

Generator

Question 32

What machines show the transfer of electrical to kinetic energy?

Answer 32

Electrical motor

Question 33

When a catapult is used to launch a paper pellet, why does the paper not keep moving forever?

Answer 33

The amount of initial elastic potential energy is finite and is transferred to a finite amount of kinetic energy in the pellet, which will move until the energy transfers into other forms such as sound and heat.