Introduction: When Tony Hawk wants to launch himself as high as possible off the half-pipe, how does he achieve this? The skate park is an excellent example of the conservation of energy. The law of conservation of energy tells us that we can never create or destroy energy, but we can change its form. In this lab, we will look at the conversion of energy between gravitational-potential energy, work, and kinetic (or moving) energy. This conversion is work. (Realize though, that in real life, skateboard wheels have friction. In our experiments, we ignore friction) Energy is measured in units of Joules. Important Formulas: Remember that numbers without units are meaningless and will receive a deduction in points. Procedure: Click on the link above for Energy Skate Park and click 1. Take some time and play with the skater and his track. 2. Click on the buttons to show the energy graphs and the pie graphs. These graphs show the conversion between kinetic energy (green) and potential energy (blue). If any energy is lost, it will be shown with a red bar (thermal energy lost). 3. Reset the skater to the standard half-pipe and observe the energy bars as he moves back and forth (without friction). 4. Bold the Correct answers! As the skater descends his kinetic energy (green) decreases / increases and his potential energy (blue) decreases / increases. The change in kinetic energy is always same / opposite to the change in potential energy. 3 pts 5. Change the skater with . Is the law of conservation of energy affected by the mass of the skater? 5 pts [No, this is because increasing the mass only increases the potential and kinetic energies, the laws remain constant no matter what the amount of the mass ] 6. Does mass of the skater affect the magnitudes of the kinetic and potential energy? 4 pts [Yes, this is because potential energy PE=mgh, thus increasing the mass increases the potential energy, also since the change in kinetic energy KE is proportional to change in PE, the KE also increases ] 7. Check the boxes to show the Potential Energy Reference (PE equal zero) and Grid lines. Reset and drag the bottom on the half pipe to the bottom of the grid to set the lowest height to zero. THIS IS IMPORTANT. 8. Left click on the PhET skater (75kg) and set him 5.0m above the zero on the ramp and allow him to skate. 9. How much potential energy does he have at 5.0m? 3654.46J 4 pts How much kinetic energy at 0.0m? 3654.46J 4 pts 10. A 20.0 kg skater that starts his skate 10m high (on the earth) would have a potential energy of _1962 joules and a kinetic energy of zero before his skate. 4 pts At the lowest point, the skater would have a potential energy of zero and a kinetic energy of 1962 joules (hint: use the important formula for potential energy) 4 pts 11. Create the skate paths as shown to the right. If the skater starts on the left side, will he have enough energy to make it all the way to the right side? No 4 pts Why? / Why not? Because the right point is at a higher level than to the left (position difference) Create the skate paths as shown to the right. If the skater starts on the left at point A, match the letter here with the following conditions: 12. Maximum kinetic energy ________B________ 2 pts 13. Maximum potential energy _______A_________ 2 pts 14. Two locations where the skater has about the same speed ______C and E__________ 4 pts 15. Create the skate paths as shown to the right. If the skater starts at the top of the ramp on the left, show how high he will be on the right side of the ramp. Try this in the simulation. Press to zoom out and increase the size of the ramp. 9.3m Part II: Gravity’s affect on Energy 16. Reset the skater and turn on the pie chart to show kinetic and potential energy. 17. Move the skater to Jupiter, where acceleration due to gravity is 26m/s2! Describe what happens to the skater’s potential and kinetic energy. 5 pts [The potential energy increases because potential energy PE=mgh, thus increasing the acceleration due to gravity (g) increases the potential energy, also since the change in kinetic energy KE is proportional to change in PE, the KE also increases] 18. Move the skater to the moon (g = 1.6 m/s2). Why is he moving like he is? 5 pts [The speed of motion is very low, this is because acceleration due to gravity is very low, Thus the change in PE is very small resulting to low velocity. These results from the fact that the change in PE= KE = 1/2*m*v²] 19. Zoom out , increase the size of the ramp, and move the skater into SPACE! Press the arrow keys on your keyboard. Zoom out some more. Have fun. 20. Is there potential (mgh) energy in space? (Note that gravity goes as 1/r2 so there never is a location in space where the acceleration of gravity is zero, but the simulation sets gravity to zero. In your answer let me now if you are using g = 0, or the rule that g goes as 1/r2) Why / Why not? 4 pts Off the surface of the moon, there’s no obvious reference point from which to measure gravitational potential energy. Conventionally, we say that an object that is an infinite distance away from the moon has zero gravitational potential energy with respect to the moon. Because a negative amount of work is done to bring an object closer to the Earth, gravitational potential energy is always a negative number when using this reference point. This is shown by the formula PE=Gm1m2/r^2 21. Is there kinetic (½mv2) energy in space? Why / Why not? 4 pts Yes , because there is PE in space given by PE=Gm1m2/r^2, also KE exists because it is dependent on PE Concluding Calculations: use g = 10. m/s2 Complete the table of kinetic and potential energies USING RED FONT FOR YOUR ANSWERS: 20 pts Mass of skater (m) height (h) velocity (v) Kinetic Energy (KE) Potential Energy (PE) 20. kg 14 m 12 m/s 1440J .2800J 60. kg 0.0 m 7 m/s 1470 J 0J 0.20 kg 18 m 0.0 m/s 0 J 36J 10 kg 6.0 m 5.0 m/s 125J 600. J 5.0 kg 17m 18.4 4m/s 160 J 850 J Conclusion Questions: use g = 10. m/s2 Bold and Underline the correct answer. Some questions have two words that need to be bolded and underlined. 1. At the highest point kinetic energy is minimum / maximum while the potential energy is minimum / maximum. 2 pts 2. At the lowest point kinetic energy is minimum / maximum while potential energy is minimum / maximum. 2 pts 3. Mass affects / does not affect the conservation of energy. 2 pts 4. How much potential energy does the 60. kg skater have before she starts her ride, 12 m above the ground? 7200J 2 pts 5. How much kinetic energy does a 60.0 kg skater have traveling with a velocity of 4 m/s? 480J 2 pts 6. How fast must a 20. kg skater travel to have a kinetic energy of 360 Joules? 6 m/s 2 pts 7. How high must a 2.0 kg basketball be thrown so it has a potential energy of 160 J? 8m 2 pts 8. How fast must the 2.0 kg basketball be thrown upward to achieve the same potential energy of 160 J? 12.65 m/s 2 pts 9. A 75kg skater starts his skate with an initial speed of 0.0 m/s, 8.0m above the ground. Just before he reaches the ground what will be his velocity? 12.65 m/s 2 pts 10. In the above question, all the potential energy became kinetic energy. How much work was done by gravity? 2 pts Zero For a custom paper on the above topic, place your order now! 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