Energy

Question 1

Where does internal kinetic energy originate from

Answer 1

The motion of particles, it is directly related to temperature and the higher the temperature the more vigorous the motion of particles

Question 2

Where does internal potential energy originate from

Answer 2

Due to the stretching and compression of intermolecular bonds as particles move. Amount of potential energy stored in bonds depends on forces between particles and distance between particles

Question 3

State four ways energy can be transferred

Answer 3

1. Mechanically by force acting over a distance
2. Heating due to a temperature difference
3. Propagation of electromagnetic waves
4. Electrically by electric current

Question 4

Describe change in energy of car as it is pushed by force F across distance s and its speed increases

Answer 4

Energy is transferred mechanically to the car by force F acting over distance s and kinetic energy of car increases.

Question 5

Describe change in energy in cup as hot water is poured into cup

Answer 5

Energy is transferred from the hotter water to the cooler cup by heating. This is due to the temperature difference between water and the cup. Internal energy of the cup increases

Question 6

Describe change in energy in water as hot water is poured into the cup

Answer 6

Energy is transferred from hotter water to the cooler surroundings and cup by heating. This is due to the temperature difference between water and surroundings and cup, so internal energy of water decreases

Question 7

Describe change in energy of solar battery charger as it is irradiated by the sun

Answer 7

Energy is transferred from the sun to the solar battery charger by electromagnetic waves, light. The chemical potential energy of battery increases

Question 8

Describe change in energy of motor when it is connected to battery and starts to spin

Answer 8

Energy is transferred electrically from the battery to the motor by electric current, so kinetic energy of motor increases

Question 9

What is the formula for kinetic energy

Answer 9

E = 1/2mv^2 where v is speed of body

Question 10

What is the formula for gravitational energy

Answer 10

E = mgh where g is gravitational field strength and h is height above reference level

Question 11

State the Principle of Conservation of Energy

Answer 11

It states that energy can neither be created or destoyed but can be converted from one form to another or transferred from one body to another. The total amount of energy in an isolated system is constant.

Question 12

Explain how principle of conservation of energy applies when a golf club hits a stationary golf ball

Answer 12

During impact, some kinetic energy of the club is converted to elastic potential energy of the ball. Some energy is transferred to surroundings as heat and sound

Question 13

What is the equation for work done

Answer 13

W = Fs, where s is distance moved in direction of force and F is force applied

Question 14

Describe how a swimmer does work on the water when swimming

Answer 14

Swimmer pushes the water backwards and water moves back a certain distance

Question 15

Describe how water does work on swimmer when swimming

Answer 15

The water pushes swimmer forward and swimmer moves forward a certain distance

Question 16

What is the equation for power

Answer 16

P = E/t, where E is energy transferred and t is time taken

Question 17

Explain why amount of electricity generated by wind turbine is less than kinetic energy from wind

Answer 17

Some of the kinetic energy is converted into heat due to friction within the turbine and sound. The wind still has some kinetic energy as not all of the mass of wind will hit the blades