Pearson Edexcel GCSE Combined Science · P8

Energy - forces doing work

50 revision questions with answers for P8 Energy - forces doing work in Pearson Edexcel GCSE Combined Science (spec 1SC0). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below. Not official Pearson material.

All 50 questions and answers

Question 1 · Spec P8.1
What is a system in an energy calculation?
Answer:
The object or group of objects chosen for analysis.
Question 2 · Spec P8.1
Name stores that can change during mechanical processes.
Answer:
Kinetic, gravitational potential, elastic potential and thermal stores.
Question 3 · Spec P8.4
How can a force change a system's energy?
Answer:
By doing mechanical work when its point of application moves through a distance.
Question 4 · Spec P8.4
How can electrical equipment change stored energy?
Answer:
Electrical work transfers energy into stores such as thermal or kinetic stores.
Question 5 · Spec P8.4
What is heating as an energy-transfer process?
Answer:
Energy transfer caused by a temperature difference, changing internal energy stores.
Question 6 · Spec P8.5
What is the relationship between work done and energy transferred?
Answer:
They are equal and both measured in joules.
Question 7 · Spec P8.6
State the work-done equation.
Answer:
Work done = force x distance moved in the force's direction, E = Fd.
Question 8 · Spec P8.6
What units must be used in E = Fd?
Answer:
Joules, newtons and metres.
Question 9 · Spec P8.6
Why use distance in the force's direction rather than any path length?
Answer:
Only displacement along the force contributes to its mechanical work in this equation.
Question 10 · Spec P8.5
Is mechanical work done by a holding force if its point of application does not move?
Answer:
No. The displacement is zero, even though a person may use energy internally.
Question 11 · Spec P8.6
A 40 N force moves a crate 3 m along the force. Find work.
Answer:
40 × 3 = 120 J.
Question 12 · Spec P8.6
A force does 150 J of work over 5 m. Find force.
Answer:
F = 150/5 = 30 N.
Question 13 · Spec P8.6
A 25 N force does 200 J of work. Find distance.
Answer:
d = 200/25 = 8 m.
Question 14 · Spec P8.7
Where does work against friction transfer energy?
Answer:
Into thermal stores of the contacting objects and surroundings.
Question 15 · Spec P8.7
What is the useful energy change when a load is lifted steadily?
Answer:
Its gravitational potential energy increases.
Question 16 · Spec P8.8
State the gravitational potential-energy change equation.
Answer:
Change in GPE = mg x vertical height change.
Question 17 · Spec P8.8
Find GPE gained by 12 kg raised 2 m, with g = 10 N/kg.
Answer:
12 × 10 × 2 = 240 J.
Question 18 · Spec P8.8
A 5 kg load gains 300 J with g = 10 N/kg. Find height.
Answer:
h = 300/(5 × 10) = 6 m.
Question 19 · Spec P8.8
A load rises 4 m and gains 800 J with g = 10 N/kg. Find mass.
Answer:
m = 800/(10 × 4) = 20 kg.
Question 20 · Spec P8.8
Why does a diagonal lifting route not change the ideal GPE gain for the same endpoints?
Answer:
GPE change depends on vertical height change, not total path length.
Question 21 · Spec P8.9
State the kinetic-energy equation.
Answer:
KE = 0.5mv².
Question 22 · Spec P8.9
Find KE of a 10 kg object at 6 m/s.
Answer:
0.5 × 10 × 6² = 180 J.
Question 23 · Spec P8.9
What happens to KE when speed triples at fixed mass?
Answer:
It becomes nine times larger.
Question 24 · Spec P8.9
What happens to KE when mass halves at fixed speed?
Answer:
It halves.
Question 25 · Spec P8.9
A 4 kg object has KE 200 J. Find its speed.
Answer:
v² = 2 × 200/4 = 100; v = 10 m/s.
Question 26 · Spec P8.1
Describe energy changes when a ball deforms on impact.
Answer:
Its kinetic store decreases as energy transfers into deformation, thermal stores and sound.
Question 27 · Spec P8.7
How much work must brakes do to stop an object with KE 900 J?
Answer:
They must transfer 900 J from its kinetic store, assuming no other energy changes.
Question 28 · Spec P8.7
A crate rises and also slides against friction. How does input work compare with GPE gain?
Answer:
Input work exceeds GPE gain because some energy is transferred to thermal stores.
Question 29 · Spec P8.3
Why must all energy transfers be considered in a closed system?
Answer:
Conservation requires the total energy before and after to be equal.
Question 30 · Spec P8.10
What does dissipated energy mean?
Answer:
Energy distributed into stores that are less useful for the intended purpose.
Question 31 · Spec P8.11
Why can mechanical devices heat up during operation?
Answer:
Work against friction transfers some energy to their thermal stores.
Question 32 · Spec P8.12
Define power.
Answer:
The rate at which energy is transferred or work is done.
Question 33 · Spec P8.13
State the power equation.
Answer:
P = E/t, or work done divided by time.
Question 34 · Spec P8.14
What does a power of one watt mean?
Answer:
One joule of energy transferred each second.
Question 35 · Spec P8.13
A winch does 4,800 J in 12 s. Find power.
Answer:
4,800/12 = 400 W.
Question 36 · Spec P8.13
A 600 W motor does 9,000 J. Find time.
Answer:
t = 9,000/600 = 15 s.
Question 37 · Spec P8.13
A 250 W device operates for 20 s. Find transferred energy.
Answer:
E = Pt = 250 × 20 = 5,000 J.
Question 38 · Spec P8.12
Two machines do equal work, but A takes half B's time. Compare powers.
Answer:
A has twice B's power.
Question 39 · Spec P8.12
Why can two people climb the same stairs with different powers?
Answer:
They may have different masses or take different times, changing energy transferred per second.
Question 40 · Spec P8.13
Convert 1.5 kW to watts before using seconds in a calculation.
Answer:
1.5 kW = 1,500 W.
Question 41 · Spec P8.15
State the efficiency equation.
Answer:
Useful energy transferred / total energy supplied.
Question 42 · Spec P8.15
A device supplies 420 J useful output from 600 J input. Find efficiency.
Answer:
420/600 = 0.70 = 70%.
Question 43 · Spec P8.15
An 80%-efficient machine receives 2,500 J. Find useful output.
Answer:
0.80 × 2,500 = 2,000 J.
Question 44 · Spec P8.15
A 60%-efficient device provides 300 J useful output. Find input.
Answer:
300/0.60 = 500 J.
Question 45 · Spec P8.15
A device receives 900 J and provides 630 J usefully. Find dissipated energy.
Answer:
900 − 630 = 270 J.
Question 46 · Spec P8.15
Can a real device have more than 100% energy efficiency?
Answer:
No. Useful output cannot exceed total supplied energy.
Question 47 · Spec P8.7
A 50 N resistive force acts over 6 m. How much energy is dissipated?
Answer:
50 × 6 = 300 J.
Question 48 · Spec P8.13
A motor raises 20 kg by 3 m in 10 s. Use g = 10 N/kg to find useful power.
Answer:
GPE gain = 600 J; useful power = 600/10 = 60 W.
Question 49 · Spec P8.15
A lift needs 1,000 J input for a 600 J GPE gain. Find efficiency.
Answer:
600/1,000 = 60%.
Question 50 · Spec P8.2
How should an energy-transfer diagram account for useful and dissipated energy?
Answer:
Show both outputs, with their total equal to the input.

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