Energy and Work ASSIGNMENT EDULABZ

Transcription

1 Energy and Work ASSIGNMENT 1. Fill in the blank spaces by choosing the correct words from the list given below : List : created, constant, destroyed, work, force, mechanical energy, displacement, K.E., electric, chemical, P.E. (i) Ability to do... is called (ii) Work is said to be done only when a... causes... in its own direction. (iii)... and... are the two basic forms of mechanical (iv) When a dry cell is connected to an electric bulb, the... energy of cell changes into... energy and light (v) The energy neither be..., nor..., and sum total of energy in a system remains a... quantity. 2. Write true or false in front of the statements given below : (i) A person standing on a road and carrying a suitcase in his hand, does work. (ii) Whenever a force causes displacement, work is said to be done. (iii) Mental energy is a kind of (iv) When the water stored in dams is made to run a turbine, the potential energy of stored water partly changes into electric (v) A falling meteor has potential as well as kinetic (vi) The energy stored in a car battery is only electric (vii) Light does not move heavy objects, and hence, is not (viii) A lady standing on one leg during an exercise, does a lot of work. (ix) Fossil fuels are wood, leaves and charcoal. (x) Magnetic energy can cause motion, and hence, is mechanical 3. Tick ( ) the most appropriate answer : (i) An aeroplane running on the runway, before taking off, has : (a) only potential energy 1

2 (b) only kinetic energy (c) both, kinetic energy and potential energy (ii) The energy stored in a car battery, has : (a) only electric energy (b) only chemical energy (c) both, electric energy and chemical energy (iii) Food digested by us, produces : (a) only muscular energy (b) only heat energy (c) both heat energy and muscular energy (iv) The source of electric energy produced at hydroelectric dam, is : (a) only potential energy of water (b) only kinetic energy of water (c) both, kinetic energy and potential energy of water (v) In petrol, solar energy is stored in the form of : (a) heat energy (b) chemical energy (c) light energy (vi) Strong current of water turns the blades of turbine, because it possesses. (a) potential energy (b) kinetic energy (c) both, potential and kinetic energy (vii) Work is said to be done, when : (a) force acts upon a body, but the body does not move. (b) force acts upon a body and moves it, in the direction of force (c) force acts upon a body, but the body does not move in the direction of force. (viii) The ultimate source of energy on the earth, is : (a) coal (b) petroleum (c) flowing water (d) sun 2

3 4. Statements given below are incorrect. Write correct statements. (i) A person holding a briefcase in his hand and standing still does work. (ii) A bird flying high in sky possesses kinetic energy only. (iii) When electric current passes through a bulb, it first changes into light and then heat (iv) When a stone is dropped from a height, its kinetic energy changes into potential (v) When the nucleus of an atom splits, the nuclear energy changes into chemical (vi) When food is digested, the chemical energy in it, changes into muscular (vii) The energy stored in a car battery, is in the form of electric (viii) Fossil fuels store energy in the form of heat (ix) Work is said to be done, when a force is applied on a body. (x) A stretched bow and arrow system possesses kinetic 5. Find odd one out. Give a reason for your choice. (i) a freely falling stone, a running train, a flying bird, water stored in a dam. (ii) wood, coal, petrol, solar cell. (iii) electric heater, electric fan, electric motor, electric generator. 6. (i) What do you understand by the term energy? (ii) Name four most common kinds of energy which you are familiar with. (iii) Name the energy used in each of the following cases : (a) Photosynthesis. (b) Making a magnet. (c) Pulling a cart. (d) Using an electric cell. (e) Boiling of milk. (f) Playing a radio. 3

4 7. (i) What do you understand by the term work? (ii) State two factors, which determine the work done by a body. (iii) Write mathematical expression for the work done by a body. (iv) State and define SI unit, in which the work is measured. (v) A body is acted upon by a force of 10 N and displacement caused is 20 m. Find the work done by the body. 8. (i) Name two situations in which a force acting on a body, does no work. (ii) Calculate the work done, when a force of 25 N moves a body through a distance of 5m. 9. (i) A force of 200 N does a work of 1000 J. Find the distance through which force acts. (ii) A body moves through a distance of 8 m and in doing so, does a work of 400 J. Find the magnitude of force acting on the body. 10. (i) Define potential (ii) Name two factors, which determine the magnitude of potential (iii) When a body falls from a height, does its potential energy increase or decrease? Give a reason for your answer. (iv) Name SI unit of potential (v) Give four examples of the bodies having potential 11. (i) Define kinetic energy (ii) Name two factors, which determine magnitude of kinetic (iii) Give four examples of kinetic 12. State, in which of the following situations, does a body possess KE or PE : (i) The stretched rubber of a catapult. (ii) A running stag. (iii) The wound up spring of an air gun. (iv) An electron revolving around nucleus. (v) A horse pulling a cart. (vi) A falling meteor. 4

5 13. (i) State the law of conservation of (ii) State all the energy changes taking place in the following cases : (a) A dry cell is connected to an electric bulb. (b) Two stones are rubbed together. (c) An alarm clock is wound and then allowed to run for 24 hours. (d) The alarm of an alarm clock starts ringing. (e) Food consumed by you. (f) Sunlight falls on green plants. (g) Petrol in the engine of a car, burns and the car rises up a steep hilly road. 14. The electric energy which is generated by burning coal is basically the solar energy of the sun. Explain the statement. 15. By giving one example, prove that the following are the forms of energy : (i) Heat (ii) Light (iii) Sound (iv) Electricity 16. (i) The diagram alongside shows a freely oscillating simple pendulum. Name the kind of energy possessed by the pendulum. (a) At A (b) In between A and B (c) At B (d) In between B and C (e) At C (ii) Name and state the law illustrated by the above observation. 5