Wednesday, 20 November 2019

WORK, ENERGY and POWER | SECTION - B QUESTIONS |


TOPIC :- WORK , ENERGY AND POWER
QUESTION BANK
SECTION - B 
(Mark - 3Each )

FOR 

SECTION - A | Work , Energy and Power  




  1. Give an example in each case where work done by a force is: (a) zero (b) positive (c) negative.
  2. A student lifts an object in the upward direction. In doing so, he applies the force on the object in the upward direction and displaces it in that direction: (However, the force of gravity is also acting on the object.)
    (a) State the direction in which force of gravity is acting on it.
    (b) Which one of these forces is doing positive work? Give reason.
    (c) Which one of these forces is doing negative work? Give reason
  3. (a) When is the work done by a body said to be negative?
    (b) An object of mass 5 kg is dropped from a height of 10 m. Find its kinetic energy, when it is half way down.
  4. A body of mass 5 kg is thrown vertically upwards with a speed of 10 m/s. What is its kinetic energy when it is thrown? Find its potential energy when it reaches at the highest point. Also find the maximum height attained by the body. (g = 10 m/s2)
  5. A force of 10 N acts on a body of 2 kg for 3 seconds. Find the kinetic energy acquired by the body in 3 seconds.
  6. (a) Define ‘potential energy’ (b) Give an example where potential energy is acquired by a body due to change in its shape.  (c) A skier of mass 50 kg stands at A at the top of a ski jump. He takes off at A for his jump to B. Calculate the change in his gravitational potential energy between A and B. 
  7. (a) Define kinetic energy.
    (b) A stone of mass 2 kg is falling from rest from the top of a steep hill. What will be its kinetic energy after 5 s? (g = 10 ms–2)
  8. A truck of mass 1800 kg is moving with a speed 54 km/h. When brakes are applied, it stops with uniform negative acceleration at a distance of 200 m. Calculate the force applied by the brakes of the truck and the work done before stopping.
  9. (a) Define kinetic energy.
    (b) The masses of scooter and bike are in the ratio of 2 : 3, but both are moving with the same speed of 108 km/h. Compute the ratio of their kinetic energy.
  10. A car weighing 1200 kg is uniformly accelerated from rest and covers a distance of 40 m in 5 seconds. Calculate the work done by the engine of car during this time. What is the final kinetic energy of car?
  11. a) An object of mass m is moving with a constant velocity v. How much work should be done on the object to bring it to rest?
    (b) Earth is revolving round the sun. What is the work done by the gravitational force exerted by the sun on earth? Justify your answer.
  12. A heavy ball falls on a thick bed of wet sand from different heights 50 cm, 1 m and 2 m respectively and the depressions created in the wet sand are carefully measured.
    (a) Which impression is the deepest and why?
    (b) Which impression is the shallowest and why?
  13. A block of known mass is placed in front of a trolley as shown in the figure. When a known mass is kept on the pan, the trolley moves and hits the block and the block gets displaced.

    (a) Where does the block get energy from?
    (b) If mass on pan is increased, will there be more work done?
    (c) What type of energy is possessed by the trolley?
  14. Explain the following phenomena in the light of your understanding of energy conversions:
    (a) How do green plants prepare food?
    (b) How does air move from place to place?
    (c) How are fossil fuels formed?
  15. With the help of an example explain the law of conversion of energy. Or State Law of Conservation of Energy and express it in the form of an equation for a body of mass m falling from a point A at height h, above the ground at (a) A, (b) B at a height from ground, (c) C. 
  16. Define power. State commercial unit and SI unit of electrical energy. An electric heater of 400 W works for 2 hours. Find the electrical energy units consumed in a day.
  17. In a house 5 bulbs of 25 W each are used for 6 hours a day. Calculate the units of electricity consumed in a month for 30 days. Also find the total expenditure if 1 unit of electricity costs Rs. 5.
  18. A lamp consumes 500 J of electrical energy in 20 seconds. What is the power of the lamp? Also find the electrical energy consumed in units if the lamp operates for 2 hours daily for 15 days.
  19. a) Define power. Give its unit.
    (b) A moving body of mass 20 kg has 40 joules of kinetic energy. Calculate its speed.
    (c) A person carrying a load of 20 kg climbs 4 m in 10 seconds. Calculate the work done and his power. (g = 10 m/s2)
  20. (a) Give one situation where force is applied but no work is done. Explain why.
    (b) A pump is used to raise water to a height of 20 m. It transfers 2000 kg of water in 15 minutes. Calculate power of the pump. [g = 10 ms–2]
  21. Water is falling on the blades of a turbine at the rate of 8 ×102 kg per minute, height of fall is 50 m. Calculate the power given to turbine. (g = 10 m/s2)
  22. A force applied on a body of mass 4 kg for 5 seconds changes its velocity from 10 m/s to 20 m/s. Find the power required.
  23. Calculate the electricity bill amount for a month of April, if 4 bulbs of 40 W for 5 hrs, 4 tube lights of 60 W for 5 hrs, a T.V. of 100 W for 6 hrs, a washing machine of 400 W for 3hrs are used per day. The cost per unit is Rs. 5.
  24. Two women Shanti and Kamla each of mass 50 kg and 60 kg respectively climb up through a height of 10 m. Shanti takes 20 s while Kamla takes 40 s to reach. Calculate the difference in the power expended by Shanti and Kamla. (Assuming g = 10 ms–2)
  25. A lamp consumes 500 J of electrical energy in 20 seconds. What is the power of the lamp? Also find the electrical energy consumed in units if the lamp operates for 2 hours daily for 15 days.

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