work+-+Energy+problems

I like to think about kinetic and potential energy as a cell phone charger. When the charger is plugged in to the wall, but not the phone, it has potential energy. When then phone is plugged in, it gives off energy that is kinetic. So that is why a cell phone charger is a great example for energy.

**Describe the difference between Kinetic Energy and Potential Energy. **


 * Potential energy is stored energy and kinetic energy is energy in motion. **

**How does it relate to what we observed using the Xpult? **


 * The potential energy on the Xpult is when the Xpult is ready to launch, but we have not launched it yet. The kinetic energy is when the Xpult shoots forward launching the perforated ping pong ball across the room. The ping pong ball flying through the air is also Kinetic energy. **

** Work is the force used to move an object some distance **

** W = F x d **

** Force needed to lift the box = 100 Newtons﻿﻿ **

** Distance needed to lift the box = 2 meters **

** 1) What work was needed to move the box 2 meters? ** ** ( N•m is considered a Joule) **


 * 200 joules is needed to move the box. **

** Mechanical Advantage = Ouput force ** ** Input force ** ** 2) The board is 30 meters long. The fulcrum is 3 meters from the Boulder and 9 meters from the person applying the force. A person applies a force of 5 newtons and the boulder is 15 Newtons. **

** What is the mechanical advantage? **


 * 3:1 is the mechanical advantage. ( this is reduced from 15N:5N the output force/input force) **

** What is the work being done by the Machine? **

Work = force (machine) x distance (machine) = 15 N x 3 m = 45 Joules

** What is the work being done by the person? **

Work = force (person) x distance (person) = 5 N x 9 m = 45 Joules

** Compare the Work of the person and machine. **

Work is the same for both the machine and the person. What makes the work easier for the person is the smaller force over a longer distance, while the machine has a larger force over a smaller distance.

** Explain scientifically why the job is easier for the person and harder for the machine. (even though the work is the same) **

What makes it easier for the person is not the work, but the reduced force by the person, that is made possible by the increased distance.

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