Work And Energy Class 9 Physics Worksheet Pdf
Class 9 Physics students should refer to the following printable worksheet in Pdf for Work And Energy in standard 9. This test paper with questions and answers for Grade 9 Physics will be very useful for exams and help you to score good marks
Class 9 Physics Worksheet for Work And Energy
CBSE Class 9 Physics Worksheet - Work & Energy (2)
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1. Under what conditions work is said to be done?
2. Derive the formula for work done by a constant force
3. Give few examples where energy is possessed by a body due to its change in shape.
4. State and prove the law of conservation of energy.
5. Is it possible that force is acting on a body but still work done is zero? Explain.
6. A rocket of mass3x106 kg takes off from a launching pad and acquires a vertical velocity of 1km/s at an altitude of 25 km. calculate (a) the potential energy and (b) the kinetic energy. (g = 9.8m/s2)
7. If a man lifts a load up with the help of a rope such that it raises the load of mass 50kg to a height of 20m in 100 sec. Find the power of man
8. A ball is dropped from a height of 5m. Find the velocity of the ball just before it reaches the ground. Do you require the value of mass to find the velocity?
9. Two persons A and B do same amount of work. The person A does that work in t1sec and the person b in t2sec. Find the ratio of power delivered by them.
10. Why do our hands become warm when rubbed against each other? Explain.
11. The kinetic energy of a body of mass 15 kg is 30J. What is its momentum?
12. Give an example for each of the following energy conversion: (1) electrical energy to kinetic energy. (2) Chemical energy to electrical energy (3) sound energy to electrical energy
13. Two bodies have same momentum. Which will have greater kinetic energy- heavier body or lighter body?
14. An electric bulb of 60w is used for 6h per day .Calculate the units of energy consumed in one day by the bulb.
15. A boy of mass 50kg runs up to a stair case of 45 steps in 9s. If the height of a step is 15cm, find his power. (g= 10m/s2)
16. Two particles of masses 1g and 2g have equal momentum. Find the ratio between their kinetic energies?
17. What will be the work done by the string, when a stone is tied to a string and whirled in a circle?
18. A locomotive exerts a force of 7500N and pulls a train through 1.5 km. How much work is done by locomotive?
19. What work a boy of mass 50kg will do in order to increase running speed from 9km/h to 18km/h.
20. The speed of a moving body is halved. What is the change in its K.E.?
21. State the energy changes taking place in the following cases: (1) A car moves up a hilly road.(2) a stone projected vertically upward returns
22.When we cut a log of wood with a saw it becomes warm, why?
23. If an electric iron of 1200W is used for 30 minutes everyday, find electric energy consumed in the month of April.
Exam Questions NCERT Class 9 Science Chapter 11 work And Energy
Question. What will happen to the kinetic energy of a body if its mass is doubled?
Ans : Its kinetic energy will be doubled.
Question. What will happen to the kinetic energy of a body if its velocity is halved?
Ans : The kinetic energy of the body will become one-fourth.
Question. When a constant force is applied to a body moving with constant acceleration, is the power of the force constant? If not, how would force have to vary with speed for the power to be constant?
Ans :We know that,
power (p) = force (f) × velocity (v)
Since the body is moving with accleration, V changes
and as a result of that P also changes, F being constant.
For P to be constant, FV = constant or F \ V
Thus, as V increases, F should decrease to keep P constant.
Question. What is the SI unit of energy?
Ans : The SI unit of energy is joule.
Question. Does a body at rest possess any kinetic energy?
Ans : No.
Question. A spring which is kept compressed by tying its ends together is allowed to be dissolved in an acid. What happens to the potential energy of the spring?
Ans : The potential energy of the spring gets converted into heat energy (kinetic energy of acid molecules). Due to this heat, the temperature of the acid rises.
Question. How much energy will an electric motor of 1 horsepower consume in one second?
Ans : An electric motor will consume 746 joule of energy per second.
Question. Give the mathematical relation between power, force and velocity.
Ans : Power (P) = force (F) × velocity (V) = (F × V)
Question. A hammer of mass 1 kg falls freely from a height of 2 m. Calculate (I) The velocity and (II) The kinetic energy of the hammer just before it touches the ground. Does the velocity of hammer depend on the mass of hammer?
Ans : PE = mgh = 1 × 9.8 × 2 = 19.6 J
PE = KE = 0.5 mv2
19.6 = 0.5 × 1 × v2
39.2 = v2
v = 6.29 m/s
No, velocity of hammer does not depend on the mass of the hammer as v = u + at
Question. Give the SI unit of potential energy.
Ans : The SI unit of potential energy is joule.
Question. What do you mean by transformation of energy?
Ans : It is the change of energy from one form of energy into another form of energy.
Question. When an arrow is shot from its bow, it has kinetic energy. From where does it get the kinetic energy?
Ans : A stretched bow possesses potential energy on account of a change in its shape. To shoot an arrow; the bow is released. The potential energy of the bow is converted into the kinetic energy of the arrow.
Question. Name at least three commonly used units of energy.
Ans : (i) Joule, (ii) Erg, (iii) Kilowatt hour.
Question. Name the practical unit of power in engineering.
Ans : Horsepower.
Question. Name at least six forms of energy.
Ans : (i) Chemical energy
(ii) Heat energy
(iii) Light energy
(iv) Electrical energy
(v) Sound energy
(vi) Solar energy
Question. How much work is done by a force of 10 N in moving an object through a distance of 4 m in the direction of the force?
Work done = Force × Displacement
= F × s
= (10 N) × (4 m)
= 40 joule or 40 J.
Question. Define potential energy.
Ans : It is defined as the energy possessed by a body by virtue of its position or change in shape.
Question. Name the energy possessed by a stretched rubber band lying on the table.
Ans : Potential energy.
Question. What is power? How do you differentiate kilowatt from kilowatt hour?
Ans : Power is the rate of doing work. Kilowatt is the unit of power and kilowatt hour is the unit of energy.
Question. Calculate the work done in lifting 200 kg of water through a vertical height of 6 m.
Ans : (i) Work done in lifting a body
= Weight of body × vertical distance
(ii) The work done in lifting
= W = mgh
= 200 kg × 10 m/s2 × 6 m = 1200 J
Question. How many watt are there in 1 horsepower?
Ans : 746 watt.
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