P1 Energy

Question 1

How do you calculate work done?

Answer 1

W = Fd
Work done (J) = Force(N) * distance moved in direction of force(m)

Question 2

How do you calculate power?

Answer 2

P = ΔE/Δt
Power(W) = change in energy(J)/change in time(s)
OR
P = W/Δt
Power(W) = work done(J)/change in time(s)

Question 3

How do you calculate efficiency?

Answer 3

Eff = useful/total
Eff. = useful energy transfer(J)/total energy transfer(J)
OR
Eff = useful power/total power

Question 4

How do you calculate the energy in a GPE store of an object?

Answer 4

Ep=mgh
Ep(J) = mass(kg) * gravitational field strength (N/kg) * height(m)

Question 5

How do you calculate the energy in the KE store of an object?

Answer 5

Ek = 1/2mv^2
Ek(J) = 1/2 * mass(kg) * velocity^2(m/s)

Question 6

How do you calculate the energy in the EPE store of an object?

Answer 6

Ee = 1/2ke^2
Ee(J) = 1/2 * spring constant(N/m) * extension^2(m)

Question 7

What is a system?

Answer 7

an object or group of objects.

Question 8

What is a closed system?

Answer 8

A system where no energy can be transferred to or from the surroundings, the total energy in the system never changes.

Question 9

What is the law of conservation of energy?

Answer 9

Within a closed system energy cannot be created or destroyed.

Question 10

What is useful energy?

Answer 10

Energy transferred where it is wanted in the way that is wanted.

Question 11

What is wasted energy?

Answer 11

Energy that is transferred to a store we did not want in a way we did not intend.

Question 12

What is dissipated energy?

Answer 12

Energy transferred to the surroundings

Question 13

What are the different pathways for energy transfer?

Answer 13

• Mechanical- forces
• Electrical-by an electric current
• Radiation-waves
• Heating-from hotter to colder object

Question 14

What are the 8 different enery stores?

Answer 14

• Kinetic-movement
• Gravitational Potential-height above ground
• Elastic Potential-deformation/extension
• Thermal-temperature
• Chemical-transferred by chemical reactions, e.g. in food
• Nuclear-stored in nuceus of atom
• Magnetic-magnetic object has when near magnet or magnetic field
• Electrostatic-charged object has when near another charged object

Question 15

What are some reasons for wasted energy and how do you reduce them?

Answer 15

• **Friction between moving parts **-lubricate moving parts
• Resistance of wires-use low resistance wires
• Air resistance/drag- streamline shape of moving object
• Sound created by machinary-tighten loose parts to reduce vibrations

Question 16

How do you answer energy transfer questions?

Answer 16

When …. , energy is transfered from the …. energy store of the …. to the …. energy store of the …. (along a(n)/the …. pathway).