Power is defined as the rate of doing work and its SI unit is the watt, so this Class 9 sheet opens with the rate definition and the unit. The answers record 3.6 × 10⁶ J for 1 kWh and 1 kWh as an energy unit.
Key Takeaways
Power is the rate of doing work (Q1).
The SI unit of power is the watt (Q2).
Q4 records 3.6 × 10⁶ J as the value of 1 kWh.
Section A: Multiple Choice Questions (1 Mark Each)
Choose the correct option for each question.
1.Power is defined as
(a) the rate of doing work(b) the total work done(c) force × distance(d) mass × acceleration
2.The SI unit of power is
(a) watt(b) joule(c) newton(d) pascal
3.The kilowatt-hour (kWh) is a unit of
(a) energy(b) power(c) force(d) electric current
4.1 kilowatt-hour is equal to
(a) 3.6 × 10⁶ J(b) 1000 J(c) 360 J(d) 3.6 × 10³ J
5.A 1000 W appliance used for 1 hour consumes
(a) 1 kWh(b) 1 J(c) 1000 kWh(d) 60 kWh
6.If two machines do the same work, the one with more power
(a) does the work in less time(b) does more work(c) uses less energy(d) works for a longer time
Section B: Short Answer Type Questions (2 Marks Each)
Show all steps clearly.
7.Define power and state its unit.
8.Write the formula for power.
9.What is one watt?
10.Define 1 kilowatt-hour.
11.What is 1 kWh equal to in joules?
12.How do you calculate the electrical energy consumed in kWh?
13.A bulb is rated 60 W. What does this mean?
14.Distinguish between energy and power.
Section C: Numericals & Word Problems (3 Marks Each)
Apply the concepts to solve the problems. Show all working.
15.A machine does 2000 J of work in 10 s. Using P = W ÷ t, find its power.
16.A motor does 9000 J of work in 30 s. Using P = W ÷ t, find its power.
17.An appliance consumes 2 kWh of energy. Using 1 kWh = 3.6 × 10⁶ J, convert this energy to joules.
18.A 100 W bulb is used for 10 hours. Using energy = power × time, find the energy consumed in kWh.
19.A 2000 W heater runs for 3 hours. Using energy = power × time, find the energy consumed in kWh.
20.A machine has a power of 500 W. Using time = work ÷ power, find how long it takes to do 2500 J of work.
Answer Key
1. a) the rate of doing work
2. a) watt
3. a) energy
4. a) 3.6 × 10⁶ J
5. a) 1 kWh
6. a) does the work in less time
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.
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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 power?
The rate of doing work, option (a) in this worksheet (Q1).
What is the SI unit of power?
The watt, option (a) in this worksheet (Q2).
How many joules are in 1 kWh?
3.6 × 10⁶ J, option (a) in this worksheet (Q4).
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