Energy Conservation Examples (KE and GPE)

Transcription

1 Name: Date: Energy onservation Examples ( and ) stunt man (m=60. kg) falls off a tower toward an airbag 50. m below.. What is the major force acting on the stunt man? Describe the work done on the stunt man as he falls.. We ll call the stunt man s initial position, and consider that and four other locations during his fall. The last one, E, is when he just barely reaches the airbag (you may want to draw this ). fter that point, he will sink into the airbag, slowing gradually enough to avoid injury, but we ll leave that off for now. Location Height (m) Speed D 30.0 E 0.0. What force acts during the fall, but we are ignoring? If we included it, how would it change the results of your calculations?. s he sinks into the airbag, what happens to the stunt man? nswer in terms of work and energy. (Note: will + still be constant?)

2 roller coaster starts at point with no kinetic energy. It then rolls along the path shown on the diagram, passing through points,, D, and E. Mass of coaster = 500 Starting Position D v = 10 m/s E kg 15 m 12 m 5 m. Notice that most of these points have their heights above the lowest level shown, but not point D, the top of the loop. The velocity of the coaster at point D is given instead. Use the information to complete the table below, showing the quantities for the coaster at each point. Location D E Height (m) Speed. We are assuming that one common force is not acting on the coaster. What is the missing force? Why are we ignoring it?. Gravity and the normal force exerted by the track are the two forces that are not being ignored. Which of these forces is not doing work, and why? D. How does this example illustrate the law of conservation of energy?

3 Name: Date: More Energy onservation Examples ( and ) pendulum starts at rest at position shown in the picture. It is released, passing through positions,, D and E in order. Notice that and D are at the same height. peg directly above the position catches the string as shown. The bob s mass is 0.50 kg. The table below lists some information about the height and speed of the bob at certain points in its motion. Use the information given to complete the table. Location Height (m) Speed D 0.2 E 0.4. Gravity and the tension force exerted by the string are the two most significant forces that act on the bob. Which of these forces is not doing work, and why?. We are ignoring one common force that probably acts on the bob. What is the missing force? Why are we ignoring it? D. How does this example illustrate the law of conservation of energy?

4 small cannon fires a 2 kg cannonball as shown. The height above the ground is shown at each point. t point the cannonball has just left the cannon, and the cannonball has 400 J of kinetic energy (). t point E the ball is just about to touch ground. Ignore air resistance. 20m 30m 20m D 10m E 0m. Use the information given to complete the table. Location Height Speed (m) 400 D E 0.0. How does this example illustrate the law of conservation of energy?

5 Name: Date: nd Even More Energy onservation Examples ( and and SPE, Oh My!) Trampoline Suppose that Kate Martenis (m = 30. kg) falls on to a trampoline. She starts her fall 5.0 m above the surface of the trampoline (point in the picture). [Note: 5 m is way too high for safety with a real trampoline!] She lands on the trampoline (point ) and then the trampoline stretches down 0.4 m, bringing her to a stop for a moment (point ) before it springs her back up. 5.4 m 0.40 m. omplete the following table for Kate s motion as she falls from to : Force Diagram Force(s) cting Work (+, 0, ) onversion Speeding Up?. omplete the following table for Kate s motion as she moves from to : Force Diagram Force(s) cting Work (+, 0, ) onversion Speeding Up?. omplete the table below. Keep in mind that when the trampoline is relaxed (that is, not stretched), then it cannot do work, so it has no energy. Location Height Speed SPE (m) D. What is the total amount of work done on Kate as she moves from point to? How do you know?

6 Simple Harmonic Oscillator You hang a metal block from a spring, and the block dangles there at rest. Then you pull the block down a few centimeters and release it. The block moves up and down, vibrating around its original, resting position. onsider the mass of the block to be 0.5 kg, and the maximum vertical displacement traveled in the vertical direction is 0.2 m.. omplete the following table for the block s motion as it moves from the bottom to the middle position. Note one change from previous versions of this activity: ompare the magnitudes of the work done by the forces. Force Diagram Force(s) cting Work (+, 0, and which is greater?) onversion Speeding Up?. omplete the following table for the block s motion as it moves from the middle to the top: Force Diagram onversion Force(s) cting Work (+, 0, and which is greater?) Speeding Up?. omplete the table below. Location Height Speed (m) SPE Top Middle ottom