( PHYSICS 1403, QUIZ 3 Chapter 6, July 31, 2007

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PHYSICS 1403, QUIZ 3
Chapter 6, July 31, 2007
Partial credit will be LIBERAL, provided that you show your work! USE BACK IF NEEDED!
(Please tell me if you’ve done so!)
Name: ______________________
1. (10 points) CONCEPTUAL QUESTIONS!! Using complete, grammatically correct,
English sentences, answer the following questions:
a. State the Work-Energy Principle. (You may supplement the sentences with equations if you
explain what each symbol means.)
b. State the Principle of Conservation of Mechanical Energy. (You may supplement the
sentences with equations if you explain what each symbol means. Note: This ISN’T the same as
the Law of Conservation of Total Energy, which states that energy can neither be created nor
destroyed but can only be transformed from one form to another!).
2. (20 points) See figure. A toy gun uses an ideal, stiff spring to shoot a dart of mass m = 0.18 kg. The
spring constant is k = 335 N/m. Neglect the dart’s gravitational potential energy in this problem (mgy
has NOTHING to do with this problem!). Hint: Be careful to take squares & square roots correctly!

x = 0.13 m
v=0
Before shooting

x=0
v=?
After shooting
a.
When the gun is cocked, the spring is compressed a distance x = 0.13 m, as in the left figure. Take
x = 0 at the end of the spring when the dart has left the gun barrel, as in the right figure. Compute
the elastic potential energy of the spring when the gun is cocked.
b.
Compute the kinetic energy of the dart just after it leaves the barrel. Compute the speed of the dart
just after it leaves the barrel. What physical principle did you use to find these results?
c.
Compute the potential energy, the kinetic energy and the speed of the dart when the spring has
moved it partway to the right to x = 0.07 m. This is not shown in the figures. It is a situation
between those shown in the two figures.
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