Chapter 8: Energy
Objectives: Define and Describe work. Define and describe power. Define mechanical energy. Define potential energy. Define kinetic energy. State the law of conservation of energy. Explain why no machines can have an efficiency of 100%
Chapter 8 Vocabulary Efficiency energy fulcrum Joule lever kinetic energy Machine work watt Pulley power potential energy Mechanical energy mechanical advantage Law of conservation of energy
What is work? So, work is the force on an object and the distance that it is moved! Measured in Joules(J). Work has two parts…… Application of force The movement of something
What is a Joule(J). The metric unit of work What is a Joule(J)? The metric unit of work. The work done with a force of 1N to move an object 1 m.
What is power? Power is the rate at which work is done! Measured in Watts (W)
Quick Question: If a forklift is replaced with a new forklift that has twice the power, how much greater a load can it lift in the same amount of time? If it lifts the same load, how much faster can it operate? Write you answer in your notes! The forklift that delivers twice the power will lift twice the load in the same time, or same load in half the time.
Energy: The property of an object or system that allows it to do work! Mechanical Energy: The energy due to the position of an object or it’s movement!
Potential Energy(PE): Stored energy http://glencoe.mcgraw-hill.com/sites/dl/free/0078600472/160350/00035807.html Measured in Joules (J)!
Kinetic Energy: Energy of motion http://glencoe.mcgraw-hill.com/sites/dl/free/0078600472/161752/00035806.html Measured in Joules (J)!
Practice Problems! How much work is done on a 100-N boulder when you lift it 1 m? What power is expended if you lift the boulder a distance of 1 m in a time of 1 s? What is the gravitational potential energy(PE) of the boulder in the lifted position?
1. How much work is done on a 100-N boulder when you lift it 1 m?
2. What power is expended if you lift the boulder a distance of 1 m in a time of 1 s?
3. What is the gravitational potential energy(PE) of the boulder in the lifted position?
Calculate the potential energy of a 8000 N piano that is raised by a pulley to the height of 10 m.
How many joules of work are done on an object when a force of 17 N pushes it a distance of 63 m?
Find the mass of a car that is traveling at a velocity of 50 m/s North Find the mass of a car that is traveling at a velocity of 50 m/s North. The car has 7,500,000 Joules of energy.
Calculate the kinetic energy of a car that has a mass of 4000 kg and is moving at 60 m/s?
A boulder is raised above the ground so that its potential energy relative to the ground is 600 J. Then it is dropped. What is its kinetic energy just before it hits the ground?
Suppose an automobile has 2000 J of kinetic energy Suppose an automobile has 2000 J of kinetic energy. When it moves at twice the speed, what will be it kinetic energy? What’s its kinetic energy at three times the speed?