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Notes: 5.2- Energy
Name: _______________________________
Energy –
Units:
Work (original definition):
Work (another definition):
Types of Energy
Non-Mechanical Energy:
Thermal Energy –
Examples:
Chemical Energy –
Examples:
Electrical Energy –
Examples:
Electromagnetic Energy –
Examples:
Nuclear Energy –
Examples:
Mechanical Energy:
Types:
1. Kinetic Energy –
Examples:
Formula:
Calculating Kinetic Energy (More practice in Practice B)
1. Calculate the amount of kinetic energy that a 1165 kg car traveling at 18.0 m/s has.
2. How much kinetic energy does Mr. Door (63 kg) have when he is running at 2.68 m/s?
3. A Boeing 747 airplane has 8.35x109 J of kinetic energy when cruising at 235 m/s. What is the mass of this
plane?
4. A normal baseball has a mass of 145g. When a good fastball is thrown, it has a kinetic energy of 116J. What
is the speed of this pitch?
Question: Which affects the Kinetic Energy of an object more? Velocity or mass? Why?
If the speed doubles, what happens to the KE?
If the mass doubles, what happens to the KE?
Work-Kinetic Energy Theorem:
Applying the W-KE Theorem:
1. Ms. Grace is being pushed by Mr. Selig with a constant force of 50.0N. How far must she push, if Mr. Selig
starts from rest, so that her final Kinetic Energy is 455N?
2. A toddler pushes a 5kg car horizontally across the floor with a constant force. If the car starts from rest and
after 0.60 meters, the car is travelling at a speed of 1.5m/s, with what force did he push it?
3. On a frozen pond, a person kicks a 10.0 kg sled, giving it an initial speed of 2.2 m/s. How far does the sled
move if the coefficient of kinetic friction between the sled and the ice is 0.10?
Read/Skim pgs.164-168 Now Try: pg. 168; Practice C
2. Potential Energy 2a. Gravitational Potential Energy –
Formula:
Examples:
Calculating Gravitational Potential energy
1. A penny with a mass of 2.5g is held on top of the Empire State Building, 381m above the ground.
How much mechanical PE does it have in this position?
2. If you want a 79g apple to have 21J of gravitational potential energy, how high off the ground do you need to hold
it?
3. An astronaut holds a 3.10kg hammer 1.5m above the surface of Mars. If the hammer has 18J of gravitational
potential energy in this position, what is the acceleration of gravity on Mars?
2b. Elastic Potential Energy –
Formula Units:
Examples:
Calculating Elastic Potential energy –
1. When a 2.00kg mass is attached to a vertical spring, the spring is stretched 10.0 cm such that the mass is 50.0
cm above the table.
a. What is the gravitational potential energy associated with this mass relative to the table?
b. What is the spring’s elastic potential energy if the spring constant is 400.0 N/m?
c. What is the total potential energy of this system?
Read/Skim pgs. 169 – 171, Now Try: pg. 172 Practice D