A constant force F moving a body a distance s along its direction does work Fs, and the kinetic energy of mass m at speed v is ½mv², so this Year 12 sheet opens with the work and kinetic energy formulas. The answers record mgh, the rate of doing work and the output-to-input power ratio.
Key Takeaways
Work done by a constant force is Fs (Q1).
Kinetic energy is ½mv² (Q2).
Q3 records mgh.
Section A: Multiple Choice Questions (1 Mark Each)
Choose the correct option for each question.
1.The work done by a constant force F moving a body a distance s in the direction of the force is...
(a) F/s(b) Fs(c) s/F(d) F + s
2.The kinetic energy of a mass m moving at speed v is...
(a) mv²(b) mgh(c) ½mv²(d) ½mv
3.The change in gravitational potential energy when a mass m is raised a height h is...
(a) mgh(b) mg/h(c) mh/g(d) mgh²
4.Power is defined as...
(a) force multiplied by distance(b) the rate of doing work(c) the energy stored in a system(d) mass multiplied by velocity
5.A 2 kg object moves at 10 m s⁻¹. Its kinetic energy is...
(a) 20 J(b) 10 J(c) 200 J(d) 100 J
6.The efficiency of a machine is...
(a) useful output power divided by input power(b) input power divided by output power(c) work input minus work output(d) total energy output per second
Section B: Short Answer Type Questions (2 Marks Each)
Show all steps clearly.
7.Define the work done by a force.
8.State the work-energy principle.
9.Define power and give its SI unit.
10.State the principle of conservation of energy.
11.Define efficiency.
12.Give one example where gravitational potential energy is converted into kinetic energy.
13.Why can a real machine never be 100% efficient?
14.State the equation linking power, force and velocity for a vehicle moving at constant speed.
Section C: Numericals & Word Problems (3 Marks Each)
Apply the concepts to solve the problems. Show all working.
15.A 50 kg box is lifted steadily through a height of 2 m. Using ΔEp = mgh with g = 9.8 m s⁻², calculate the gain in gravitational potential energy.
16.A 1000 kg car travels at 20 m s⁻¹. Using Ek = ½mv², calculate its kinetic energy.
17.A 5 kg object is dropped from rest through a height of 20 m. Assuming energy is conserved, use v = √(2gh) with g = 9.8 m s⁻² to calculate its speed just before impact.
18.A motor lifts a 200 kg load through a height of 3 m in 10 s. Using P = mgh/t with g = 9.8 m s⁻², calculate the useful power output.
19.A constant horizontal force of 100 N pushes an object 5 m in the direction of the force in 4 s. Calculate the work done and the average power.
20.A car engine delivers 60 kW of power at a steady speed of 30 m s⁻¹. Using P = Fv, calculate the driving force.
Answer Key
1. b) Fs
2. c) ½mv²
3. a) mgh
4. b) the rate of doing work
5. d) 100 J
6. a) useful output power divided by input power
7. Refer to solution guide.
8. Refer to solution guide.
9. Refer to solution guide.
10. Refer to solution guide.
11. Refer to solution guide.
12. Refer to solution guide.
13. Refer to solution guide.
14. Refer to solution guide.
15. Refer to solution guide.
16. Refer to solution guide.
17. Refer to solution guide.
18. Refer to solution guide.
19. Refer to solution guide.
20. Refer to solution guide.
End of Worksheet
People Also Ask
What is the work done by a constant force F over a distance s?
Fs, option (b) in this worksheet (Q1).
What is the kinetic energy of mass m at speed v?
½mv², option (c) in this worksheet (Q2).
What is power?
The rate of doing work, option (b) in this worksheet (Q4).
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