1.        Select “Friction” in the Energy Skate Park: Basics HTML5 simulation. You should see a U-shaped track with a skateboarder nearby. Check the “Pie Chart”, “Bar Graph”, “Grid”, and “Speed” boxes. Leave the Mass and Friction sliders in their default middle positions. Drag and drop the skateboarder to the highest point on the left side (the red dot underneath the skateboarder should be right at a height of 6 m), then release the skateboarder. Observe the motion of the skateboarder as she skates back and forth for 30 seconds or more. Describe the skateboarder’s motion. What changes, if anything? Why? Be sure to invoke principles of energy conservation.

2.        In which of the following scenarios is no work done? Select all that apply!

           A barbell is lifted from the ground to overhead.

           A barbell is lowered from overhead to the ground.

           A barbell sits on the ground.

           A barbell is held overhead in place..

3. 53000 J of work is done on a 1400 kg car by its brakes, bringing it to a stop in 6.61 m. What force does the brakes apply to the car?