WORK, ENERGY and POWER | SECTION - C QUESTIONS |

TOPIC :- WORK , ENERGY AND POWER

QUESTION BANK

SECTION - C 

(Mark - 5Each )

CONTINUE ...........

SECTION - A | WORK , ENERGY and POWER

SECTION - B | WORK , ENERGY and POWER

1. What do you mean by work? Give an example of negative work done. What is the work to be done to increase the velocity of a car from 18 km/h to 90 km/h if the mass of the car is 2000 kg? 
2. (a) Define work. Give SI unit of work. Write an expression for positive work done. (b) Calculate the work done in pushing a cart through a distance of 50 m against the force of friction equal to 250 N. Also state the type of work done. (c) Sarita lives on 3rd floor of building at the height of 15 m. She carries her school bag weighting 5.2 kg from the ground floor to her house. Find the amount of work done by her and identity the force against which she has done work (g = 10 ms^–2)
3. (a) Define kinetic energy of an object. Can kinetic energy of an object be negative? Give reason.
   (b) A car weighing 1200 kg is uniformly accelerated from rest and covers a distance of 40 m in 5 seconds. Calculate the work, the car engine had to do during this time.
4. (a) Derive an expression for kinetic energy possessed by an object of mass m, moving with velocity v. Also state the SI unit of kinetic energy.
   (b) A ball of mass 400 g rolls on a ground with uniform speed of 25 m/s. Find the kinetic energy possessed by it.
5. (a) Justify that “a body at a greater height has larger energy”.
   (b) A body of mass 2 kg is thrown up at a velocity of 10 m/s. Find the kinetic energy of the body at the time of throw. Also, find the potential energy of the body at the highest point. The value of g = 10 m/s².
6. (a) Give reason for the following:
   (i) The kinetic energy of a freely falling object increases, yet it holds law of conservation of energy.
   (ii) A girl fills up 10 pages of a notebook in order to practise sums, yet she has not done ‘work’ in terms of Science/Scientific concept.
   (iii) Work done by gravitational force on an object moved along a horizontal path, is zero.
   (b) Find the energy in kWh consumed in 24 hours by two electric devices, one of 100 W and other of 500 W.
7. (a) State the principle of conservation of energy. What are the various energy transformations that occur when you are riding a bicycle?
   (b) A body of mass 25 g has a momentum of 0.40 kg m/s. Find its kinetic energy.
8. What is meant by energy? How is energy related to work done? A person pushes a wall and fails to move it. What is the work done? Why does he get tired?
9. (a) Two bodies of equal masses move with uniform velocities v and 3v respectively. Find the ratio of their kinetic energies.
   (b) Define power. An electric heater is rated 1500 W. How much energy does it use in 10 h? Express your answer in (i) kWh (ii) joules
10. (a) A ball thrown vertically upwards returns to the thrower. How do the kinetic and potential energies of the ball change?
    (b) Calculate the power of a pump which lifts 100 kg of water to a water tank placed at a height of 20 m in 10 s. (Given g = 10 ms^–2)
11. (a) State the law of conservation of mechanical energy.
    (b) Explain the conservation of energy in case of a freely falling object.
    (c) Find the velocity of a body of mass 2 kg having kinetic energy of 100 J.
12. Read the graph depicting change in height of an object with time.
    (a) Explain the changes in components of total mechanical energy with reasons.
    (b) Find the velocity with which the object is projected.
    (c) Find the maximum height achieved by the stone if it takes 4 s to reach that height.
    (d) Find out the maximum P.E. of the stone if its mass is 200 g.
13. (a) Define 1 kWh.
    (b) A crane is lifting a body to a height h in time t. Find the relation between the power of crane to the speed at which it is lifting the object.
    (c) If an electric iron of 1600 W is used for 45 minutes everyday, find the electric energy consumed in the month of March.

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