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PH1110
Term A07
STUDY GUIDE 3:
Work, Energy, and Momentum
Objectives
15. Define work and calculate the work done by a constant force as the body on which it acts is moved
by a given amount.
Be able to calculate the scalar product of two vectors.
16. Define kinetic energy.
17. State the workenergy theorem. Give examples of and solve problems for which the application of the
workenergy theorem is appropriate.
18. Define power, and use the concept to solve problems involving the rate at which work is done.
19. Distinguish between conservative and nonconservative forces and give examples of each.
20. Calculate the work done on a particle by a uniform gravitational force and by a spring undergoing
compression or extension.
21. Use the principle of mechanical energy conservation to solve appropriate problems.
22. Define the linear momentum of a particle and of a system of particles.
23. Define impulse of a force and relate it to the change in linear momentum that it causes.
24. Give examples of and solve problems for which conservation of linear momentum is appropriate.
Distinguish between elastic and inelastic collisions.
Suggested Study Procedure for Chapter 6.
Study
Secs. 6.1 through 6.4.
Study
Examples 2, 3, 4, 6, 7.
Answer
Questions 2, 5, 11, 12, 13.
Do
Exercises 3, 4, 17, 25, 29, 33, 37.
Do
Problems 57, 62, 69, 82, 91.
A.
As great as we have already found Newton's laws to be in helping us understand and predict the
motion of objects, there are wondrous new and enormously powerful concepts lurking in those three
disarmingly simple statements.
Two such concepts that tumble mathematically right out of the 2nd
law are WORK and ENERGY, the subjects of Chapts. 6 and 7.
1. A FORCE carried through a DISPLACEMENT performs WORK.
But be careful here!
Work is
NOT force times distance; rather, it involves only the component of force parallel to the
displacement.
In the special case of straightline displacement with constant force (the case we
will consider most of the time!), work is equal to the product of the force component parallel to
the displacement with the distance traveled.
2. Work and energy are SCALAR quantities  they are purely numbers WITHOUT spatial direction.
DO NOT attach vector directions to work or energy; that's just plain WRONG!
Now it may
bother you that a scalar can result from the multiplication of two vector quantities (force and
displacement), but that's the way it is.
The mathematical operation that accomplishes this strange
feat is called the "scalar product" and is discussed in detail in Sec. 6.1.
Sections 6.1 through 6.3
provide discussion and worked examples on the subject.
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The WORKENERGY THEOREM (which comes mathematically straight out of the 2nd law!) states
that the TOTAL WORK done on an object is equal to the CHANGE IN KINETIC ENERGY of the
object
(final minus initial).
What's so great about that, you may ask?
Well, for one thing, a scalar
equation is invariably easier to work with than a vector equation.
For another,
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This note was uploaded on 04/29/2008 for the course PH 1110 taught by Professor Kiel during the Fall '08 term at WPI.
 Fall '08
 Kiel
 Energy, Force, Momentum, Work

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