Download Work Problems

Policastro/Finizio
Contemporary Physical Science
Period 4
Quiz Date: 1/12/05
Pendulum Problems, Work Problems, and Section 15.1
Study Guide
Formulas
1. Potential Energy = mass  gravity  height
*Remember Gravity always equals 9.8
*Unit for Potential Energy is Joules
2. Kinetic Energy =
1
 mass  velocity 2
2
*unit for Kinetic Energy is the Joule
3. Force = weight ( Kg )  10
*unit for Force is the Newton
4. Work =
force  dis tan ce
*unit for work is the Joule
Section I: Kinetic/Potential Energy Problems
Sample Problem #1
Calculate the kinetic energy of a 1kg toy car traveling at a constant velocity of 2 m/s.
Step #1: Determine what Formula to use. This question asks us to
calculate Kinetic Energy. Therefore we will use the following formula.
1
 mass  velocity 2
2
*In order to calculate the Kinetic Energy, you must plug your numbers into the formula.
Mass = 1kg
Velocity = 2 m/s
KineticEnergy 
1
(1)(2)
2
Kinetic Energy = 1 Joule
Sample Problem #2
Find the Velocity of a Pendulum using the given data.
Mass: 3 Kg
Height: 1 meter
Step #1: Find the Potential Energy of the Pendulum. In order
to do this use the following formula. P.E. = (m)(g)(h)
Potential Energy = (3)(9.8)(1)
Potential Energy = 29.4 Joules
Step #2: Since we are looking for Velocity we can use the Kinetic Energy
formula. Place the Potential Energy you found in for Kinetic Energy. Set it up
as follows
1
29.4   m  v 2
2
29.4 
1
 3  v2
2
Step #3: Solve this equation for V. In order to
do this you must isolate the V
29.4 
1
 3  v2
2
29.4 
3
2
3 2
v
2
3
2
Divide both sides by
19.6  v 2
19.6  v2
4.43  v
Final Answer
3
2
Section II. Work Problems
What is the work done by a weight lifter who lifts a 1600-newton barbell over his head?
Assume that the barbell is lifted to a height of 2.0 meters.
Formula Needed: Work =
force  dis tan ce
In this problem:
Force = 1600 N
Distance = 2.0 m
Therefore the Equation you must set-up is:
Work = 1600  2.0
Work = 3200 Joules
Section III: Section 15.1
Key Terms
 Energy
 Kinetic Energy
 Potential Energy
 Gravitational Potential Energy
 Elastic Potential Energy
 Mechanical Energy
 Thermal Energy
 Chemical Energy
 Electrical Energy
 Electromagnetic Energy
 Nuclear Energy
Key Points
 Energy is the ability to do work.
 When work is done on an object, energy is transferred to that object.
 The energy of motion is called Kinetic Energy.
 Potential Energy is energy that is stored as a result of position or shape
 An objects potential energy depends on its mass, its height, and the acceleration
due to gravity.
 The potential energy of an object that is stretched or compressed is known as
Elastic Potential Energy.
 The energy associated with motion and position of everyday objects is
mechanical energy.
 The total potential and kinetic energy of all the microscopic particles in an object
make up its thermal energy.
 Chemical Energy is the energy stored in chemical bonds.
 Electrical Energy is the energy associated with electric charges
 Electromagnetic Energy is a form of energy that travels through space in the
form of waves
 The energy stored in atomic nuclei is known as Nuclear Energy.
 The unit of energy is the Joule.
Practice Problems
1. Calculate the kinetic energy of a 0.25-kg toy car traveling at a constant velocity of
2 m/s.
2. Calculate the potential energy of a 3-kg pendulum that is held 2 m in the air.
3. Calculate the Kinetic energy of a 1.5 kg remote control car that is traveling at a
constant velocity of 5 m/s.
4. Calculate the velocity of a pendulum using the following data.
a. Mass = 2 kg
b. Height = 2 meters
5. Calculate the velocity of a pendulum using the following data.
a. Mass = 4 kg
b. Height = 5 meters
6. John has an object suspended in the air. It has a mass of 50 kilograms and is 50
meters above the ground. How much work would the object do if it was dropped?
7. Calculate the work done by a weight lifter who lifts 100 kilograms 2 meters off
the ground.
*In addition to this study guide be sure to study
all class notes and assignments. This includes the
reading and questions that you did in Section 15.1
of your Textbook. *