Topic 8

Question 1

8.3
What happens to the total energy of a closed system when energy changes are happening in it?

Answer 1

No net change

Question 2

8.4
Identify 3 different ways the energy of a system can be changed

Answer 2

-Work done by forces
-Electrical equipment
-Heating

Question 3

8.5
What is the energy transferred equal to?

Answer 3

Work done

Question 4

8.6
State the equation for work done. Add units

Answer 4

Work done (J) = Force (N) × distance (m)
E=F×d

Question 5

8.6
Define the term work done

Answer 5

Energy transferred by force across distance

Question 6

8.8 8.9
When an object falls, not all the GPE is transferred to KE. Why is this?

Answer 6

-Object subject to air resistance
-As fall, air resistance does work
-Thermal energy transferred to air/surroundings

Question 7

8.10
What will happen to some of the energy in all system changes

Answer 7

Dissipate -> stored in less useful ways e.g. thermal

Question 8

8.11
When does a mechanical process become wasteful

Answer 8

When cause rise in temp -> dissipate thermal energy to surroundings

Question 9

8.12
Define the term power

Answer 9

r. E transferred per second
(rate of doing work if energy transferred by forces)

Question 10

8.12
State 2 factors that will affect power

Answer 10

-Energy
-Time

Question 11

8.13
State the equation for power

Answer 11

Power (W) = Work done (J) / Time (s)
P=E/t

Question 12

8.14
What is 1 Watt equal to?

Answer 12

1 J/s

Question 13

Two girls want to climb some stairs. One decides to run up them and the other walks up, will one use more energy than the other? Explain why and comment on their power.

Answer 13

-Energy = same
-Bc work done = same
-E=F×d d=same F=same
-Power = diff
-P=E/t E=same t=diff
-Running girl used more P bc climbed at faster rate