Conservation and dissipation of energy

Question 1

What are the eight ways in which energy can be stored?

Answer 1

1. Chemical
2. Kinetic
3. Electrostatic
4. Gravitational potential
5. Elastic potential
6. Thermal (internal)
7. Magnetic
8. Nuclear

Question 2

Which four ways can energy be transferred?

Answer 2

1. Mechanically
2. Electrically
3. By radiation
4. By heating

Question 3

What changes in energy stores occur when an object falls?

Answer 3

1. The object speeds up as it falls.
2. Energy is transferred from the object’s gravitational potential energy store to its kinetic energy store mechanically (by force).
3. Its gravitational potential energy decreases but its kinetic energy increases.

Question 4

What energy transfers happen when a falling object hits the ground without bouncing back?

Answer 4

1. The object’s kinetic energy store is transferred to the thermal energy store of the object and the floor by heating (and by sound waves).

Question 5

What changes in energy stores occur when an object is thrown into the air?

Answer 5

1. The object slows down as it goes up.
2. Energy is transferred from the object’s kinetic energy store to its gravitational potential energy store mechanically (by force).
3. Its kinetic energy decreases but its gravitational potential energy increases.

Question 5

Show the energy transfers and changes in energy stores in a torch lamp using a flow diagram.

Answer 5

Chemical energy store in the battery
V
Electric current in the waves
V
Energy transferred to the surroundings
V
Light waves
+
Increase in thermal energy store of the surroundings.

Question 6

How does height affect gravitational potential energy?

Answer 6

The higher an object is in the air, the more gravitational potential energy it has.

Question 7

Show the energy transfers and changes in energy stores for an object fallings and hitting the ground using a flow diagram.

Answer 7

Gravitational potential energy store
V
Kinetic energy store
V
Energy transferred to the surroundings
V
Sound waves
+
Increase in thermal energy store of the surroundings.

Question 8

A climbing centre wants to know the speed that a climber would reach the floor if they fell from a height of 6.5m, so they can fit the floor with the right amount of protective foam. Work out the speed.

Answer 8

1. Gravitational potential energy is involved.
2. Kinetic energy is involved.
3. Gravitational potential energy store transfers to the kinetic energy store.
4. Work out the velocity

6.5m is the initial height.
0m is the final height.
G.p.e = mgh
kinetic energy = 0.5mv²

g.p.e = kinetic energy
mgh = 0.5mv²

gh = 0.5v²
gh / 0.5 = v²
v = √gh / 0.5
v = √10 x 6.5 / 0.5
v = 11.4 m/s

Question 9

A student pushes a sprung biro on the table vertically and lets go. As a result, the pen jumps vertically and reaches its highest point before falling down on the table again.
Describe how energy is transferred when the pen has reached its highest point in the jump.

Answer 9

1. Energy is transferred from the elastic potential energy of the sprung biro to the kinetic energy store of the pen mechanically.
2. As the pen goes up, it slows down.
3. The kinetic energy store transfers to the gravitational potential energy store mechanically.
4. The kinetic energy decreases but the gravitational potential energy increases until it has reached its maximum gravitational potential energy.