Your Name
Recitation Instructor's Name:
Recitation Section #:
Physics 112
March 3, 2005
Prelim Exam #1
7:30  9 PM
PLEASE BE SURE THIS PACKET HAS 12 PAGES
!
(
This includes the cover sheet and a scrap page.)
This packet contains 6 Short Answer Questions, 3 Problems, a page of scrap paper, and a
page of Possibly Useful Information.
Write your answers ON THESE QUESTION SHEETS in the spaces provided.
For Short Answer Questions #16, ONLY ANSWERS WILL BE GRADED, unless
calculations or constructions are explicitly requested.
For Problems #79, where algebra or computations are required, BE SURE YOUR
METHOD OF SOLUTION IS CLEAR, and SHOW YOUR WORK in the spaces provided.
If
you need more space, use the backs of the question sheets and indicate the whereabouts of
your work for each question.
ANSWERS WITHOUT WORK will NOT receive credit
(except for short answer questions).
WORK ON SCRAP PAPER WILL NOT BE GRADED.
Point values for questions are given by each problem and below.
BUDGET YOUR TIME.
Don't spend too much time on any one question or part of a question.
Answer those
questions you can do easily first, and then return to the more difficult ones.
It is valuable
use of your time to READ THE ENTIRE EXAM before starting to work on it.
This is a CLOSED BOOK and CLOSED NOTES exam.
You may NOT use any other
references or personal assistance.
You MAY use a NONGRAPHING calculator.
You may NOT use energy methods.
For Grading Only:
13
/14
7
/24
4
/8
8
/12
5
/10
9
/24
6
/8
TOTAL
/100
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Your Name
2
SHORT ANSWER
[40 points]
Please mark
letters
of your answers in spaces provided.
1.
[4 points]
Two boys, Abe and Bob, decide to race identical sleds down a frictionless
hill.
Abe + his sled have a mass of 50 kg, while Bob + his sled have a mass of 60 kg.
(a)
If both Abe and Bob start from rest at the same time at the top of the hill, who
should reach the bottom of the hill first?
(Ignore friction and air resistance.)
(A)
Abe
(B)
Bob
(C)
They both reach the bottom at the same time.
Answer:
Now the boys attach identical rocket engines to their sleds and race across level
horizontal frictionless snow.
If they start from rest at the same time and place, who wins
the race?
(Again, ignore friction and air resistance.)
(A)
Abe
(B)
Bob
(C)
They both reach the finish line at the same time.
Answer:
2.
[5 points]
Three
identical ideal springs,
each having spring
constant k, are connected
as shown.
What is the
effective spring constant
of this combination of springs?
(A)
k/3
(D)
k
(G)
2k
Answer:
(B)
k/2
(E)
4k/3
(H)
3k
(C)
2k/3
(F)
3k/2
3.
[5 points]
Shown is a portion of the graph of the
vertical velocity v
y
(t) vs. time t for a beach ball of
weight
w
that was tossed vertically into the air.
The
slope of the graph at points #13 has the values:
slope #1
=
 0.7 g
slope #2
=
 0.6 g
slope #3
=
 0.5 g
(a)
What is the magnitude of the
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 Fall '07
 LECLAIR,A
 Physics, mechanics, Force, normal contact force

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