The SI unit of work is the joule and the SI unit of power is the watt, so this Class 9 sheet opens with the two units of the chapter. The answers record ½mv² for kinetic energy, mgh for potential energy and 20 J.
Key Takeaways
The SI unit of work is the joule (Q1).
The SI unit of power is the watt (Q2).
Q3 records ½mv².
Section A: Multiple Choice Questions (1 Mark Each)
Choose the correct option for each question.
1.What is the SI unit of work?
(a) newton(b) joule(c) watt(d) pascal
2.What is the SI unit of power?
(a) joule(b) watt(c) newton(d) joule-second
3.The kinetic energy of a body of mass m moving with velocity v is
(a) mv(b) ½mv²(c) mv²(d) 2mv²
4.The potential energy of an object of mass m raised to a height h above the ground is
(a) mgh(b) mgh²(c) mg ÷ h(d) m ÷ gh
5.According to the law of conservation of energy, energy
(a) can be created(b) can be destroyed(c) can be transformed from one form to another(d) remains constant only in machines
6.A boy lifts a book of mass 1 kg to a shelf 2 m high. The work done against gravity is (g = 10 m/s²)
(a) 5 J(b) 10 J(c) 20 J(d) 2 J
Section B: Short Answer Type Questions (2 Marks Each)
Show all steps clearly.
7.Define work. When is work said to be done by a force?
8.Write the SI unit of work and define one joule.
9.Define kinetic energy and write its formula.
10.Define potential energy and write its formula.
11.State the law of conservation of energy.
12.Define power and write its SI unit.
13.When is the work done by a force zero? Give one example.
14.What is the commercial unit of energy? Give its relation with the joule.
Section C: Numericals & Word Problems (3 Marks Each)
Apply the concepts to solve the problems. Show all working.
15.A force of 20 N acts on a body and displaces it through 5 m in the direction of the force. Find the work done. (W = F × s)
16.A body of mass 2 kg is moving with a velocity of 4 m/s. Find its kinetic energy. (KE = ½mv²)
17.An object of mass 5 kg is raised to a height of 10 m. Find the potential energy gained. (g = 10 m/s², PE = mgh)
18.A motor of power 500 W works for 20 seconds. Find the work done by the motor. (W = P × t)
19.A body of mass 1 kg is thrown vertically upward with a velocity of 20 m/s. Find its kinetic energy at the instant of throwing and the maximum height it reaches. (KE = ½mv², g = 10 m/s²)
20.A pump lifts 100 kg of water to a height of 20 m in 10 seconds. Find the work done and the power of the pump. (g = 10 m/s², W = mgh, P = W ÷ t)
Answer Key
1. b) joule
2. b) watt
3. b) ½mv²
4. a) mgh
5. c) can be transformed from one form to another
6. c) 20 J
7. Refer to solution guide.
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20. Refer to solution guide.
End of Worksheet
People Also Ask
What is the SI unit of work?
The joule, option (b) in this worksheet (Q1).
What is the SI unit of power?
The watt, option (b) in this worksheet (Q2).
What is the formula for kinetic energy?
½mv², option (b) in this worksheet (Q3).
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