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Presentation On Work And Power

Home > PowerPoint Slides > Presentation On Work And Power
Published in: Physics
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This PPT is suitable for the IGCSE and O Level Physics students. It only provides theoretical background of the topic. The practice questions, worksheets and topical questions will be discussed during the tutoring sessions

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  1. Work & Power Physics (IGCSE / O-Level)
  2. What will you learn in this lesson? • Work • Calculating mechanical work • Power • Calculating Power
  3. Work To lift an object, you need a store of energy (as chemical energy, in your muscles). You give the object more gravitational potential energy (g.p.e.). The force is your means of transferring energy from you to the object. The name given to this type of energy transfer by a force is doing work. work done energy transfrrred While applying breaks to a bicycle the kinetic energy (k.e.) of the cycle is reduced. Which force reduces the k.e.? Where the k.e. is transferred to which form of energy?
  4. Work (contd.) The amount of energy transferred by a force depends on two things: • the size of the force — the greater the force, the more work it does • the distance moved in the direction of the force — the further it moves, the more work it does. VV=AE AE = change in energy
  5. Calculating Mechanical Work • Work is dependent on Force and distance. So, • Since this is the same as the amount of energy transferred, it is measured in joules (J), the unit of energy. • The relation between Joules and Newtons is IJ=1Nx1m=1Nm
  6. Calculating Mechanical Work (contd.) The weight or force is pointing downwards. So, it will be calculated as Work done - energy transferred by gravity = g.p.e. = mgh Can you explain gravitational potential energy is the work done by gravitational pull? Calculated the work done if the child is 25 kg and height (h) is 5 m. How do you explain the energy transfer? h It is important to use the correct distance when calculating work. Gravity makes the child slide down the slope. However, to calculate energy transferred by gravity height (h) will be considered
  7. Calculating Work (contd.) • How much work she is doing in raising the box? • How much g.p.e. does the box gain? • Compare the two energies and comment on their difference. 2ØN
  8. Power The rate at which work is done or the rate at which energy is transferred is called Power. Sl unit of power is Watt (W) Here are two ways you can increase your power: • lift a heavier object in the same time • lift the object more quickly. Your neighbor is lifting bricks and placing them on top of a wall. He lift s them slowly, one at a time. State two ways in which he could increase his power (the rate at which he is transferring energy to the bricks).
  9. Calculating Power pow er 1000 W = 1 kW (kilowatt) 1 000 000 W 1 tv1W (megawatt) Power rating is used to find the efficiency of electrical device such as bulbs IEofuI p:mer output percentage efficiency = x 100% input How the unit of power can be Nm/s?
  10. Calculating Power (contd.) One horsepower is the power output of one horse when it lifts a mass of 33000 1b of water through a height of one foot in one minute At— 1 min Ah 1 foot t 330001b You nud to knowthat 1 1b = 0.453592 kg and one foot = 0.3048 metros. a b c d Calculate the mass of water the horse lifts in one minute. Calculate the weight of water the horse lifts in one minute. (Assume that g Calculate the work the horse does in one minute. Calcclate the pcnver output of the horse. 10 Wkg)

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