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Potential Energy And Kinetic Energy


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Potential Energy And Kinetic Energy

  1. 1. Potential energy and kinetic energy Coming down the hill
  2. 2. Potential and Kinetic Energy <ul><li>Reviewing last weeks experiment </li></ul><ul><li>Using the potential energy converting into kinetic energy design a roller coaster </li></ul><ul><li>Finding the length of the track </li></ul><ul><li>Calculating the time over the track </li></ul><ul><li>Velocity time graph </li></ul><ul><li>Calculating the electrical energy/ power of the motor needed to pull up your ride </li></ul>
  3. 3. Trolleys down a slope Potential energy changing to kinetic energy Set up the trolleys going down the slope Measure the height to the top of the slope Calculate the velocity at the bottom of the slope using the formula Attach the ticker-tape to the back of the trolley Feed it through the ticker-tape machine The ticker tape puts a mark down every 0.2 seconds Calculate the speed at the bottom of the slope Velocity = distance/time Do the two answers match? - repeat for different heights Band at bottom to stop trolley V = 2gh
  4. 4. Potential energy Potential energy is all about how high you are off the ground It is the amount of work gravity can do on you if you fell e.g. If you are higher up, you can fall further. P e = mgh m = mass g = gravity (10 on Earth) h= height from the bottom (how far the fall is)
  5. 5. Kinetic energy Kinetic energy is all about movement If you are moving you have kinetic energy Heavy things moving have more kinetic energy Fast objects have more kinetic energy K e = ½ m V 2 m = mass V = Velocity
  6. 6. pendulum The pendulum coverts potential energy into kinetic energy and back again It never quite gets back to the top as you lose some energy in friction Good in clocks All the potential is turned in kinetic energy Pe = Ke mgh = ½ m V 2 gh = ½ V 2 V = 2gh The velocity at the lowest point can be calculated by this formula
  7. 7. Rules of the rollercoaster design The first hill provides the potential energy by pulling your cart up with a motor The speed of the rollercoaster must not go over 90 km/h (60mph) – 25 metres/s (that is the record speed for a rollercoaster) You must have enough speed to get up the next hill To make it easy the track is frictionless The truck weighs 800 Kg Work out the maximum height for the first hill first Each square on the graph paper = 5 metres
  8. 8. Steps to go through <ul><li>Draw the roller coaster track with the 5 parts– rise, fall, run off, hill, loop </li></ul><ul><li>Each square = 5m </li></ul><ul><li>Find the height of the 4 peaks and calculate potential energy P e = mgh </li></ul><ul><li>Calculate the velocity at the bottom of the first slope </li></ul><ul><li>Calculate the velocity at the top of the other 3 high points </li></ul><ul><li>To do this you need to know the kinetic energy at the bottom of the slope and the potential energy at the top – there will be a difference in this number </li></ul><ul><li>The difference will be the energy still contained as kinetic energy </li></ul><ul><li>Use the kinetic energy formula to calculate the velocity V = 0.5mv 2 </li></ul><ul><li>6) Find the length of your 5 sections of track by using a piece of string </li></ul><ul><li>7) Calculate the time it takes to go through each section </li></ul><ul><li>Time = distance/speed (average speed on the slope is needed) </li></ul><ul><li>The fist slope starts a V=0M/s and ends at 25m/s, the average speed will be 12.5 m/s </li></ul>Mass of coaster = 800kg V = 2gh
  9. 9. Make a velocity time graph for your coaster Speed at top of hill 2 Can be calculated by Ke at bottom of slope – Pe at top of slope The remaining energy must all be kinetic use the kinetic energy formula The area under the graph is the total length of your track
  10. 10. What is the electrical energy needed to pull your coaster to the top of the hill E = ItV THE ENERGY NEEDED WILL BE THE SAME AS THE POTENTIAL ENERGY What will the power of the motor be if it takes a minute to pull the coaster to the top P = IV
  11. 11. What uses are there for changing potential energy into kinetic energy