3. One of the graphs that we can look at is the energy as a function of position. Toggle the energy graph back to energy vs. position. Does the horizontal axis represent the x-coordinate? Or does it represent the distance that the skater has traveled along the track? Figure out a way to convincingly decide the answer to this question and describe both what the answer is and why you think so. won obermoo, todd. wow 4. Another place where the simulation is ambiguous is in the friction: notice that there are no numbers on the "Friction" slider! From playing with the simulation quantitatively, figure out what the scale is. Determine the friction coefficient for at least two different non-zero values of the friction so you can say whether the scale is likely to be linear or not. 2 Energy Graphs to (gvoda nwode as) and ofloddaisy and cut taskpochistar "ONup but no i In the figure below is shown a w-shaped track. Five points along the track are marked with small circles (labeled A-F). The zero for the gravitational potential energy was taken at point C. The skateboarder starts at rest at the point labeled A and then then starts rolling down the track. For this problem, ignore friction and the rolling effects of the (small) wheels. 1. At which point on the track do you think the following bar graph was taken? Justify your answer. Total Kinetic Thermal Potential2. The graph below shows the skateboarder's various energies as functions of time. Where is the skate- boarder on the track at the various instants indicated? 1000 0 N Figure 2: Total is yellow; P.E. is blue; K.E. is green; thermal is red. 3. The skateboarder's mass is 60 kg. If they are moving with a speed of 5.5 m/s as they pass through point C, 3.1 meters above the lowest point on the track, how much higher is point A above the lowerst point?TN this worksheet, we'll use the Energy Skate Park PhET simulation to help us think about mechanical energy. In this simulation, you can set up the track and simulate a skateboarder rolling along the track. The simulation provides many tools including: grab points to change the shape of the track; grids and rulers to help you quantify the motion; multiple graph- ical representations including bar charts, pie charts, and line graphs; toggles that allow you to adjust friction, mass, gravity, and other parameters. It's good to take a few minutes to familiarize your- Figure 1: Source: PhET Energy Skate Park; self with the simulation if you've not already done www.phet.colorado.edu So. 1 Exploring the Sim 1. On the "intro" interface, set up the parabolic track (as shown above) and place a skater on the track letting them roll back and forth. Turn on the "pie chart" option and toggle the energy bar graph. Observe this a few times. Try it with and without friction. Toggle the "reference height" (at the bottom of the screen) and try a few different heights. Which graphical representation of the energy division helps you best understand what's going on? There is no "correct" answer here; we simply want you to think critically about different representations. 2. Is this simulation quantitatively correct? Click over to the "graphs" window, adjust the graph so that it plots energy vs. time, and set up a simple enough situation that you can calculate the initial and final energies of the skateboarder. Compare your values to the graph of energy vs. time and make a convincing enough case that the simulation is or is not quantitatively correct