HW4__Chap_4
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HW4: Chap 4
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HW4: Chap 4
Due: 11:59pm on Tuesday, October 24, 2023
You will receive no credit for items you complete after the assignment is due.
Grading Policy
Pulling Three Blocks
Three identical blocks connected by ideal (massless) strings are being pulled along a horizontal frictionless surface by a horizontal force
. The
magnitude of the tension in the string between blocks B and C is
= 3.00
. Assume that
each block has mass
= 0.400
.
Part A
What is the magnitude
of the force?
Express your answer numerically in newtons.
Hint 1.
Find the acceleration of block B
What is the magnitude
of the acceleration of block B?
Express your answer numerically in meter per second squared.
Hint 1.
Consider blocks A and B as a unit
Since blocks A and B are not moving with respect to each other, you can treat them as one larger "object." This larger object has
the same acceleration as either block A or block B alone. The advantage of such an approach is that the larger object has only one
force acting on it (the tension 3.00
in the rope).
ANSWER:
Hint 2.
Find the acceleration of all three blocks
Which of the following expressions gives the magnitude
of the acceleration of the three blocks?
Hint 1.
Consider all three blocks as a unit
Since the three blocks are not moving with respect to one another, you can treat them as one larger "object" of mass equal to the
sum of the masses of all three blocks. The only horizontal force acting on this larger object is
, so you can use Newton's 2nd law
to determine an expression for its acceleration.
ANSWER:
= 3.75
Typesetting math: 100%
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HW4: Chap 4
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ANSWER:
Correct
Part B
What is the tension
in the string between block A and block B?
Express your answer numerically in newtons
Hint 1.
How to approach the question
The tension
is the only horizontal force acting on block A. Thus, you can find the acceleration of block A and then apply Newton's 2nd
law. Note that all three blocks have the same acceleration.
ANSWER:
Correct
Problem 4.61
A 2.5
block is placed on a frictionless table. The block is connected by massless ropes over massless pulleys to a 7.5-
block on the right, and a
3.0-
block on the left, as shown in .
= 4.50
= 1.50
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HW4: Chap 4
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Part A
Find the acceleration of the block on the table.
Express your answer with the appropriate units.
ANSWER:
Correct
Problem 4.55
The figure shows a block (mass
) on a smooth horizontal surface, connected by a thin cord
that passes over a pulley to a second block
, which hangs vertically.
Part A
Draw a free-body diagram for block A, showing the force of gravity on it, the force (tension) exerted by the cord, and any normal force.
Draw the vectors starting at the black dot. The location and orientation of the vectors will be graded. The exact length of your vectors
will not be graded but the relative length of one to the other will be graded.
ANSWER:
=
3.4
Typesetting math: 100%
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Correct
Part B
Draw a free-body diagram for block B, showing the force of gravity on it, the force (tension) exerted by the cord, and any normal force.
Draw the vectors starting at the black dot. The location and orientation of the vectors will be graded. The exact length of your vectors
will not be graded but the relative length of one to the other will be graded.
ANSWER:
No elements selected
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Correct
Part C
Apply Newton's second law to find the formula for the acceleration of the system. Ignore friction and the masses of the pulley and cord.
Express your answer in terms of the variables
,
, and appropriate constants.
ANSWER:
Correct
Part D
Apply Newton's second law to find the formula for the tension in the cord. Ignore friction and the masses of the pulley and cord.
Express your answer in terms of the variables
,
, and appropriate constants.
ANSWER:
No elements selected
=
=
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Correct
Problem 4.52
A 480-
piano is being unloaded from a truck by rolling it down a ramp inclined at 20
. There is negligible friction and the ramp is 13.0
long. Two
workers slow the rate at which the piano moves by pushing with a combined force of 1200
parallel to the ramp.
Part A
If the piano starts from rest, how fast is it moving at the bottom?
Express your answer using two significant figures.
ANSWER:
Correct
Problem 4.40
At the instant a race began, a 61-
sprinter exerted a force of 800
on the starting block at a 23
angle with respect to the ground.
Part A
What was the horizontal acceleration of the sprinter?
Express your answer using two significant figures.
ANSWER:
Correct
Part B
If the force was exerted for 0.31
, with what speed did the sprinter leave the starting block?
Express your answer using two significant figures.
ANSWER:
Correct
Problem 4.74
= 4.7
= 12
= 3.7
Typesetting math: 100%
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Two equal masses in contact on a frictionless surface are acted on by the forces
and
as shown in .
Part A
Determine the magnitude of the contact force exerted on each mass by the other when
.
Express your answer as a multiple of
.
ANSWER:
Correct
Part B
Determine the magnitude of the contact force exerted on each mass by the other when
.
Express your answer as a multiple of
.
ANSWER:
Correct
Part C
Determine the magnitude of the contact force exerted on each mass by the other when
Express your answer as a multiple of
.
ANSWER:
Correct
Problem 4.73
= 1
= 0.75
= 0.5
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HW4: Chap 4
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A parent pulls his child in a wagon across a floor. The child and wagon have a combined mass of 35
. The wagon handle is inclined at 55
to the
horizontal, and the child and wagon (whose wheels are nearly frictionless) are accelerating at 0.32
.
Part A
With what force is the parent pulling on the wagon handle?
Express your answer with the appropriate units.
ANSWER:
Correct
Problem 4.77
Part A
In the figure , if
=1.50
,
= 1.40
and =33.0 , what will be the
magnitude of the acceleration of the system?
ANSWER:
Correct
Part B
Which direction will the
move?
ANSWER:
Correct
Part C
If
=1.50
and the system remains at rest, what must the mass
be?
= 20
= 1.97
Up the incline
Down the incline
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ANSWER:
Correct
Part D
Calculate the tension in the cord for Part A.
ANSWER:
Correct
Part E
Calculate the tension in the cord for Part C.
ANSWER:
Correct
Problem 4.83
An elevator in a tall building is allowed to reach a maximum speed of 3.3
going down.
Part A
What must the tension be in the cable to stop this elevator over a distance of 3.0
if the elevator has a mass of 1400
including occupants?
Express your answer using two significant figures.
ANSWER:
Correct
Score Summary:
Your score on this assignment is 100%.
You received 9 out of a possible total of 9 points.
= 0.817
= 11.0
= 8.01
= 1.6×10
4
Typesetting math: 100%
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