2.2 Energy Transfer Examples

Question 1

Conservation of energy law

Answer 1

Energy cannot be created or destroyed. It can only be transferred from one form to another.

Question 2

Describe how energy is transferred when coal burns

Answer 2

• Coal has a large store of chemical energy (energy within chemical bonds)
• When coal is burned the chemical energy is transferred by heating to the thermal energy store of the coal.
• Hot coals and flames transfer energy to the surroundings by heating and radiation.

Question 3

Describe how energy is transferred when a car is breaking

Answer 3

• The moving car has kinetic energy.
• The brakes mechanically do work on the car to slow it down.
• The kinetic energy of the car decreases and the thermal energy store of the brakes increases.

Question 4

Describe how energy is transferred when an archer is firing a bow and arrow

Answer 4

• As the string of the bow is pulled back, chemical energy in the archers muscle is transferred mechanically to the elastic potential of the bow.
• When the archer releases the string of the bow, the elastic potential energy of the string is transferred mechanically to the kinetic energy store of the arrow.

Question 5

Which energy store increases when an object is lifted 1.5m above the ground?

Answer 5

Gravitational potential

Question 6

A ball is lifted 1.5m above the ground has 20 J of gravitational potential energy. The ball is dropped. What is the kinetic energy of the ball just before it hits the ground?

Answer 6

20 J