Today, we are transitioning into talking about energy and are going to start small and examine energy from a few different scenarios. These scenarios highlight the idea of choosing systems and will ask you to analyze each problem from two different systems. This will hopefully help you all compare and contrast these two different approaches to solving energy problems.
Project 7: Learning issues
- Relationship Between Force and Energy - Work
- Choosing a system
- Conservation of Energy
- Potential and Kinetic Energy
Scenario 7a: Captain America slows down a train
There is a train speeding down a track with a constant velocity of 20.9 m/s, which appears to have malfunctioning breaks. Captain America gets in front of the train and slows the train to a stop before the train runs over the cliff. Consider this situation from the time Captain America starts slowing the train down until the train comes to a stop.
Choice 1: System = train + Captain America + Earth Choice 2: System = train
1. For each choice of system above, answer the following questions:
- Is energy conserved in the system? Why/why not?
- Is work done on the system? Is it positive or negative? How do you know?
- Draw the energy bar charts for the scenario.
2. Pick a system to calculate how much force Captain America must apply to slow the train down in 750 m.
3. Which system did you choose for your analysis? Why?
Scenario 7b: Iron Man speeds up a train
Iron Man encounters a train that has run out of fuel 1000 m before the train station. He decides to put on his blasters (which have a force of 2000 N), and he pushes the train for 500 m to get it up to speed. He's hoping that friction for the rest of the way will slow down the train by the time it arrives at the station.
Choice 1: System = train + iron man + Earth Choice 2: System = train
1. For each choice of system above, answer the following questions:
- Is energy conserved in the system? Why/why not?
- Is work done on the system? Is it positive or negative? How do you know?
- Draw the energy bar charts for the scenario.
2. Pick a system to calculate how fast the train will going when it gets to the station.
3. Which system did you choose for your analysis? Why?
Scenario 7c: Hawkeye Launches Arrow
Hawkeye is standing the edge of a tall building (80 m) and needs to fire an arrow into the sky as a warning to the other avengers. He releases the arrow with an initial speed of 50 m/s at an angle of 60 degrees. Consider this situation from the instant after the arrow is launched.
Choice 1: System = Arrow + Earth Choice 2: System = Arrow
1. For each choice of system above, answer the following questions:
- Is energy conserved in the system? Why/why not?
- Is work done on the system? Is it positive or negative? How do you know?
- Draw the energy bar charts for the scenario.
2. Pick a system to calculate the maximum height that the arrow will reach in the sky.
3. Which system did you choose for your analysis? Why?
Scenario 7d: Spiderman drops an apple
Spiderman is chilling on top of a skyscraper (120 m) eating his lunch, when he accidentally drops his apple. The apple then plummets toward an unsuspecting people on the street below.
Choice 1: System = Apple
Choice 2: System = Apple + Earth
1. For each choice of system above, answer the following questions:
- Is energy conserved in the system? Why/why not?
- Is work done on the system? Is it positive or negative? How do you know?
- Draw the energy bar charts for the scenario.
2. Spiderman decides to shoot a web to try to catch the apple before it hits a person on the street. Pick a system to calculate how much work Spiderman must do to stop the apple before it hits someone.
3. Which system did you choose for your analysis? Why?
Scenario 7e: Captain Marvel lowers the In finity Gauntlet
In the midst of the battle with Thanos, Captain Marvel obtains the very precious infi nity gauntlet (m = 2 kg). When she finds it, she raises the gauntlet above her head in victory but then realizes that may be a poor idea considering all the bad guys around. She then lowers the gauntlet again. Consider this time period, when Captain Marvel raises then lowers the infi nity gauntlet.
Choice 1: System = In finity Gauntlet
Choice 2: System = In finity Gauntlet + Earth
1. For each choice of system above, answer the following questions:
- Is energy conserved in the system? Why/why not?
- Is work done on the system? Is it positive or negative? How do you know?
- Draw the energy bar charts for the scenario.
2. When Captain Marvel lowers the in finity gauntlet, how much work does she do?
3. Which system did you choose for your analysis? Why?
Project 7g: Hulk Trap
Black Widow unfortunately finds the Hulk trapped in a net by the ceiling, which is tied to an anchor on the floor. Black Widow wants to rescue the Hulk but doesn't want him mad at her for just dropping him directly to the floor. If the Hulk weighs 566 kg, how much weight should the Black Widow attach to the other end of the rope so that the Hulk will land on the ground with a speed of 3 m/s?