Work Done and Energy Transfer

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Work Done and Energy Transfer

  1. 1. Work and Energy CCEA Physics page 9
  2. 2. Learning Intentions <ul><li>By the end of the lesson we will be able to… </li></ul><ul><li>Define the term ‘work done’ using it correctly in the context of physics </li></ul><ul><li>Recall the equation for work done, including the units </li></ul><ul><li>Calculate work done in a number of simple experiments </li></ul>
  3. 3. I’VE BEEN WORK ING ALL FREAKIN’ DAY!!! Some people work harder than others… In Science the word ‘ work ’ has a very definite meaning… Even Jack ‘I always stop the terrorists’ Bauer knows that energy and work are interrelated!!
  4. 4. By definition <ul><li>Work is defined as a force acting upon an object to cause a displacement </li></ul><ul><li>For example, a horse doing work by pulling a cart- the force is provided by the horse and the displacement is the distance the cart moves </li></ul>F d
  5. 5. Now your turn… <ul><li>Draw on the Force and the Displacement for the three examples- </li></ul>F d F F F d Is it an example of work?
  6. 6. Calculating Work <ul><li>The equation for working out work (…see what I did there?) is simply- </li></ul>Work = Force x Displacement Wee note- The displacement needs to be in the same direction as the force W = F x d Word Equation Dimensions Units Joules = Newton x metre
  7. 7. Using the equation <ul><li>Example 1 </li></ul><ul><li>Take 1 kg weight = 10 newtons </li></ul><ul><li>Calculate the work done when… </li></ul><ul><li>A mass of 5 kg is lifted 50 cm, </li></ul><ul><li>A mass of 300 g is lifted 150 cm. </li></ul><ul><li>a) Force = 5 x 10 = 50 N </li></ul><ul><li>Distance = 0.5 m </li></ul><ul><li>Work Done = 50 x 0.5 </li></ul><ul><li>= 25 J </li></ul><ul><li>Try b) by yourself </li></ul><ul><li>Ans. Work Done = 4. 5 J </li></ul>
  8. 8. Work Done
  9. 11. Exercise 1 <ul><li>Complete the following questions by yourself </li></ul><ul><li>A lift of mass 250 kg carries a man of mass 76 kg. How much work is done by the wire rope which draws the lift through a height of 15 m? </li></ul><ul><li>A man walks up a hill of incline 30 º for 150 metres. If his weight is 750 N, how much work has he done against gravity? </li></ul>30 150 150 sin 30 = 75 metres 48900 J or 48.9 kJ 56250 J or 56.25 kJ
  10. 12. The force in the equation is linked to the mass, how? What is the total force in the question? What is the ‘work done’ equation Put the values of the force (in Newtons) and the distance (in metres) into the equation Work Done- steps needed to complete the example question 1 2 3 4

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