Energy

Question 1

define a system

Answer 1

an object or a group of objects

Question 2

what happens when a system changes?

Answer 2

there are changes in the way energy is stored

Question 3

Describe all changes involved when an object projected upwards

Answer 3

an object slows down as it goes up. Here the energy is transferred from the object’s kinetic energy store to its gravitational potential energy store

Question 4

Describe all changes involved when a moving object hitting an obstacle

Answer 4

causes energy to be transferred from the car’s kinetic energy store to other energy stores like elastic potential and thermal energy stores of the car object and the body

Question 5

Describe all changes involved when Bringing water to boil in a kettle

Answer 5

energy is transferred to the water by heating, into the water’s thermal energy store (causing the temperature to rise)

Question 6

what is the formula to find the kinetic energy of an object?

Answer 6

Ek = ½ mv^2

Question 7

what is the formula to find the gravitational potential energy

Answer 7

Ep = mgh

Question 8

define power

Answer 8

rate at which energy is transferred OR the rate at which work is done

Question 9

what is the formula to find power?

Answer 9

Power = energy transferred /time
P = w/ t

Question 10

what is the conservation law?

Answer 10

Energy can be stored, transferred or dissipated but cannot be created or destroyed

Question 11

give an example of how in all system energy is dissipated so that it is stored in less useful ways?

Answer 11

For example, in a moving car, energy from the fuel is converted into kinetic energy to propel the vehicle, but some of the energy is dissipated as heat due to friction with the road and air resistance.

Question 12

give 2 ways and an explanation on how to reduce unwanted energy transfers

Answer 12

a) lubrication - using lubricants between moving parts reduces friction, which in turn reduces the amount of energy lost as heat

B) insulation - minimize heat transfer to the surroundings. This is particularly useful in buildings to reduce heat loss in winter or heat gain in summer

Question 13

give the formula to find efficiency

Answer 13

Efficiency = useful output energy transfer / total input energy transfer

Question 14

what are some ways to increase the efficiency of an intended energy transfer

Answer 14

reducing friction, minimizing resistance, or optimizing the design of the system to minimize energy dissipation

Streamlining the process eliminating unnecessary steps, reducing resistance or drag, or optimizing the flow of energy through the system.

Question 15

give 2 effects that an increase in the temperature of an object will have on the radiation that it emits

Answer 15

• the radiation’s intensity will increase
• the wavelength distribution of the radiation will change

Question 16

True or false? Parallel light rays reflecting off a rough surface are scattered in different directions because the angle of incidence isn’t always equal to the angle of reflection. Explain your answer.