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Physics 53
Summer 2009
1
Exam I
Solutions
Part A:
Multiple choice questions. Check the best answer.
1.
The total mechanical energy of a particle:
Always decreases if nonconservative forces do work. [Can increase]
Is always positive.
Changes by the total amount of work done by all forces. [Only non
conservative forces]
√
Is constant if only conservative forces do work.
2.
Shown are trajectories for three projectiles launched with the
same
initial speed.
Which of the following is NOT true?
#1 reaches its target in the least time.
#3 stays in flight the longest.
The elevation angles at launch for #1 and #2 add to 90°.
√
A projectile launched at an angle between those of #1 and #2 will not go
as far as either of those. [Farther]
1
2
3
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View Full Document Physics 53
Summer 2009
2
3.
In the situation shown, a block is being dragged across a rough floor by pulling
on the rope with force
T
. The coefficient of kinetic friction is
μ
k
. The force of
friction on the block has magnitude:
k
mg
k
T
sin
!
√
k
(
mg
!
T
sin
"
)
Cannot be determined without knowing the block’s acceleration.
4.
The total potential energy for a combination of conservative forces is given by
U
(
x
)
=
x
2
!
2
x
. Which of the following is NOT true?
The system has only one point of static equilibrium, at
x
=
1
.
The formula for the total force is
F
x
=
2
!
2
x
.
√
The equilibrium at
x
=
1
is unstable. [Stable]
If the total energy is zero, there are turning points at
x
=
0
and
x
=
2
.
Part B:
Truefalse questions. Mark each sentence with T of F. Each question has a value of 3 points.
1.
The purpose of a simple machine (such as an inclined plane or a lever) is to do
the same work with a smaller force over a larger distance.
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This note was uploaded on 10/19/2011 for the course PHYSICS 53L taught by Professor Mueller during the Spring '07 term at Duke.
 Spring '07
 Mueller
 Physics, Energy, Force, Work

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