2 Mechanical Equilibrium
An object in mechanical
equilibrium is stable, without
changes in motion.
2 Mechanical Equilibrium
Question: Warm UP
• How can you change an object’s state of
motion?
2 Mechanical Equilibrium
Question: Warm UP
• How can you change an object’s state of
motion?
• Answer: An unbalanced force is needed
to change an object’s state of motion.
2 Mechanical Equilibrium
2.1 Force
Net Force
A force is a push or a pull.
To change the motion of an object, you need an
unbalanced force.
A force of some kind is always required to change the
state of motion of an object.
The combination of all forces acting on an object is
called the net force. The net force on an object
changes its motion.
The scientific unit of force is the newton, abbreviated N.
2 Mechanical Equilibrium
How Forces affect Motion
•
•
•
•
•
•
Make things start moving.
Make objects move faster.
Make objects move slower.
Make objects stop moving.
Make Objects change direction.
Make objects change shape.
2 Mechanical Equilibrium
Force Facts
•
•
•
•
Forces are measured in Newtons, (N).
Forces act in pairs.
Forces act in a particular direction.
Forces usually cannot be seen, but their
effects can.
• Science uses vectors to visualize the
magnitude and direction of forces.
2 Mechanical Equilibrium
Common forces that affect motion of
objects.
•
•
•
•
•
•
•
•
Mechanical, including friction
Electrical charges
Nuclear
Magnetic
Elastic-spring
Heat
wind
Chemical
2 Mechanical Equilibrium
2.1 Force
Net Force
When the girl holds the
rock with as much force
upward as gravity pulls
downward, the net force
on the rock is zero.
2 Mechanical Equilibrium
2.1 Finding Net force of an object
The table pushes up on
the book with as much
force as the downward
weight of the book. The
net force of the book is
zero.
2 Mechanical Equilibrium
2.1 Force
Showing Forces using Force Vectors
A vector is an arrow that represents the magnitude and
direction of a force.
A vector quantity needs both magnitude and direction for a
complete description. Force is an example of a vector quantity.
2 Mechanical Equilibrium
Drawing 1-D force vectors
• A vector is drawn using an arrow. The
length of the arrow indicates the
magnitude of the vector. The direction of
the vector is represented by no
surprisingly, the direction of the arrow.
• Magnitude is the strength of the force,
measured in Newton’s here.
• Direction in this class is U, D, L & R.
2 Mechanical Equilibrium
Warm-Up Question (Vectors)
• An object has a mass of 500 g.
– What is the weight (force) in Newton’s of the
500 g mass? Predict and then measure using
a spring scale.
– How do you Draw a vector that shows both
the magnitude and direction of the 500 g
mass accurately. Predict and explain and
then draw.
• Scale is 1cm = 1Newton
2 Mechanical Equilibrium
Warm-Up Question Solution
• An object has a mass of 500 g.
– What is the force in Newton’s of the mass?
• 5 Newton’s
– Draw a 1-dimensional vector of the force, with
both magnitude and direction.
• Scale is 1cm = 1Newton
– 5 cm long arrow, 5 N magnitude, downward direction
2 Mechanical Equilibrium
2.1 Force
Force Vectors
1 cm = 20 N
This vector represents a force of 60 N to the right.
2 Mechanical Equilibrium
Draw Vectors of these masses on Graph sheet.
Activity: Hang mass using spring scale, find the force in
Newton's, (N), and then draw vectors for each mass on
piece of graph paper.
Make sure to draw the arrow tail (beginning) and head
(end) of each vector.
100 g = 1 N
1 N = 1 cm
Mass (g)
100
300
400
700
900
1000
Force (N)
Vector Length
(cm)
2 Mechanical Equilibrium
55 Kg man!
1Kg = 1N
10 N = 1cm
1. Identify the two types of forces acting on this man as he hangs
in the air cleaning windows.
2. What is the net force on this man?
2 Mechanical Equilibrium
1. Identify the two types of forces acting on this guy up in the
air. How many vectors? Explain
Upward force & downward force. The force due to tension on the
rope holding man up, and the weight of the man due to gravity.
2 Mechanical Equilibrium
Write down these words and definitions
Support force: An upward force that has the same
magnitude as a force due to gravity (weight) but is
opposite in direction.
Downward force: Any force acting
downward due to gravity, (weight).
Resultant force: The combination of all
forces acting on an object.
The resultant force (net force) is always
determined by finding the sum (∑) of all
the forces.
2 Mechanical Equilibrium
Write down these words and definitions
• Mechanical equilibrium: When the sum of
all forces on an object is equal to zero; no
change in motion or at rest!
• Displacement: The difference between the
initial position (start)of an object and any
later position (end).
2 Mechanical Equilibrium
Chapter 2 Support Force-Warm up
The table pushes up on the book with
as much force as the downward
weight of the book.
?N
This book has 5 N downward force
(weight) due to gravity.
What is the upward force (support
force)? Explain
5N
What is the resultant force?
Explain
2 Mechanical Equilibrium
Chapter 2 Support Force-Warm up
+5N
-5N
+5N + (-5N) = 0N
The table pushes up on
the book with as much
force as the downward
weight of the book.
This book has 5 N
downward force due to
gravity.
What is the upward
force? Explain 5N U, 5N D
What is the resultant
force? Explain 0N, no
Direction
2 Mechanical Equilibrium
Force
Net Force
The net force depends on
the magnitudes and
directions of the applied
forces.
∑ = sum
Net force is, ∑ Forces = ?
2 Mechanical Equilibrium
Force
Net Force
The net force depends on
the magnitudes and
directions of the applied
forces.
2 Mechanical Equilibrium
Force
Net Force
The net force depends on
the magnitudes and
directions of the applied
forces.
2 Mechanical Equilibrium
Force
Net Force
The net force depends on
the magnitudes and
directions of the applied
forces.
2 Mechanical Equilibrium
Force
Net Force
The net force depends on
the magnitudes and
directions of the applied
forces.
2 Mechanical Equilibrium
Force
Net Force
The net force depends on
the magnitudes and
directions of the applied
forces.
2 Mechanical Equilibrium
Force
Tension and Weight
A stretched spring is under a “stretching force”
called tension.
Pounds and Newton's are units of weight, which
are units of force.
2 Mechanical Equilibrium
Force
Tension and Weight
The upward tension in the
string has the same magnitude
as the weight of the bag, so the
net force on the bag is zero.
The bag of sugar is attracted to
Earth with a gravitational force
of 2 pounds or 9 newtons.
2 Mechanical Equilibrium
Force
Tension and Weight
There are two forces acting on the bag of sugar:
• tension force acting upward
• weight acting downward
The two forces on the bag are equal and opposite. The
net force on the bag is zero, so it remains at rest.
2 Mechanical Equilibrium
Force
Force Vectors
2 Mechanical Equilibrium
Bridges and Forces
• Objective: I will understand how forces are
distributed in real world structures, such as
bridges. I will design a bridge that must
withstand the greatest force among all
groups in class!
2 Mechanical Equilibrium
Question:
• What was the greatest force your bridge
design held up today with or without
collapsing?
• What basic bridge type held the most
forces before collapsing, if it did collapse?
2 Mechanical Equilibrium
Force
How can you change an object’s state
of motion?
2•
Mechanical Equilibrium
•0 km away
•Q. Dropping supplies, a plane flies 700 km west one day. The next day it flies 600 km east. Then it flies 300 km west and on the next day 400 km east. How
Question of the day-Exit ticket
• Adding vectors to find resultant vector!
• 1 cm = 100 km
• Dropping supplies, a plane flies 700 km west
one day. The next day it flies 600 km east.
Then it flies 300 km west and on the next day
400 km east. How far away (displacement) is
the plane from where it first began? Explain!
2 Mechanical Equilibrium
Question of the Day
Looking for a nesting site, a bird flies 7 km west one day. The next day it flies 6 km south. Then it flies 3
km east and on the next day 4 km north. How far away is the bird from where it first began?
4.47 km away
2 Mechanical Equilibrium
Question of the Day-Warm-up
Prediction and then Verify.
2 Mechanical Equilibrium
Question of the Day-Warm-up
Answer and Solution
C, D, A=B
2 Mechanical Equilibrium
Question of the day
• For an object to be in equilibrium, what must be
true?
• The painters and scaffolding are in equilibrium,
so what is the unknown force acting downward?
2 Mechanical Equilibrium
Question of the day Solution
• For an object to be in equilibrium, what must be true?
Things must be steady, nothing is changing.
• The painters and scaffolding are in equilibrium, so what
is the unknown force acting downward? 400 N
• The sum of the upward vectors equals the sum of the
downward vectors is
, & is in static equilibrium.
2 Mechanical Equilibrium
LOVE Card Review
• Please take out LOVE cards.
– Or make LOVE cards if you lost them.
• Quiz each other for 5-minutes.
– Matching, verbal, study quietly, etc..
• I will stop by and give each student a
grade for completing your cards.
2 Mechanical Equilibrium
2.2 Mechanical Equilibrium
What is the Mechanical Equilibrium
rule?
2 Mechanical Equilibrium
2.2 Mechanical Equilibrium
Mechanical equilibrium is a state oif steadiness, and
nothing is changing.
Whenever the net force on an object is zero, the object
is in mechanical equilibrium—this is known as the
equilibrium rule.
2 Mechanical Equilibrium
2.2 Mechanical Equilibrium
• The  symbol stands for “the sum of.”
• F stands for “forces.”
For a suspended object at rest, the forces acting upward on
the object must be balanced by other forces acting
downward.
The vector sum equals zero.
2 Mechanical Equilibrium
2.2 Mechanical Equilibrium
The sum of the upward vectors equals the sum of the
downward vectors. F = 0, and the scaffold is in equilibrium.
2 Mechanical Equilibrium
2.2 Mechanical Equilibrium
The sum of the upward vectors equals the sum of the
downward vectors. F = 0, and the scaffold is in equilibrium.
2 Mechanical Equilibrium
2.2 Mechanical Equilibrium
think!
If the gymnast hangs with her weight evenly
divided between the two rings, how would scale
readings in both supporting ropes compare with
her weight? Suppose she hangs with slightly
more of her weight supported by the left ring.
How would a scale on each rope read?
2 Mechanical Equilibrium
2.2 Mechanical Equilibrium
think!
If the gymnast hangs with her weight evenly
divided between the two rings, how would scale
readings in both supporting ropes compare with
her weight? Suppose she hangs with slightly
more of her weight supported by the left ring.
How would a scale on the right read?
Answer: In the first case, the reading on each
scale will be half her weight.
2 Mechanical Equilibrium
2.2 Mechanical Equilibrium
You can express the equilibrium rule
mathematically as F = 0.
2 Mechanical Equilibrium
Question of the Day-Warm-up
Where does the garbage can need to be located so
the see-saw will be level and in mechanical
equilibrium? Show your work and all units..
2 Mechanical Equilibrium
Question of the Day-Warm-up
Where does the garbage can need to be located so
the see-saw will be level and in equilibrium? Show
your work and all units..
Answer: 1.5 Meters
2 Mechanical Equilibrium
Question of the Day-Smart Ropes Lab
In the above diagram, the 1 Kg mass will hang on
the ruler. If you slide the 1Kg mass across the
ruler, causing spring scale 1 tension force to
decrease 5 N, what will spring scale 2 do? Make
prediction and explain your thinking!
Hint: think about upward/downward net force!
2 Mechanical Equilibrium
Question of the Day-Smart Ropes Lab
In the above diagram, the 1 Kg mass will hang on
the ruler. If you slide the 1Kg mass across the
ruler, causing spring scale 1 tension force to
decrease 5 N, what will spring scale 2 do? Make
prediction and explain your thinking!
Solution: To keep forces balanced, spring scale 2
will increase by 5-newtons.
2 Mechanical Equilibrium
Question of the Day-Net Force
• Four different students, student A, B, C, and D,
pull from four different directions. Which student
will end up pulling the blue square in their
direction?
• a. student A b. student B
• c. student C d. student D
2 Mechanical Equilibrium
Question of the Day-Net Force
• Four different students, student A, B, C, and D,
pull from four different directions. Which student
will end up pulling the blue square in their
direction?
• a. student A b. student B
• c. student C d. student D
2 Mechanical Equilibrium
Question of the Day-Warm-up
•What position does the 80 kg man need to
be located at, so the beam is balanced?
2 Mechanical Equilibrium
Question of the Day-Solution
2 Mechanical Equilibrium
2.3 Support Force
For an object at rest on a horizontal surface, the
support force must equal the object’s weight.
2 Mechanical Equilibrium
2.3 Support Force
What forces act on a book lying at rest on a table?
• One is the force due to gravity—the weight of the book.
• There must be another force acting on it to produce a net
force of zero—an upward force opposite to the force of
gravity.
The upward force that balances the weight of an object on a
surface is called the support force.
A support force is often called the normal force.
2 Mechanical Equilibrium
2.3 Support Force
The table supports the book with a support force—
the upward force that balances the weight of an object
on a surface.
A support force is often called the normal force.
2 Mechanical Equilibrium
2.3 Support Force
• The upward support force is positive and the downward
weight is negative.
• The two forces add mathematically to zero.
• Another way to say the net force on the book is zero is
F = 0.
The book lying on the table compresses atoms in the table and
they squeeze upward on the book. The compressed atoms
produce the support force.
2 Mechanical Equilibrium
2.3 Support Force
The upward support
force is as much as the
downward pull of
gravity.
2 Mechanical Equilibrium
2.3 Support Force
The upward support
force is as much as the
downward pull of
gravity.
2 Mechanical Equilibrium
2.3 Support Force
think!
What is the net force on a bathroom scale when a 110-pound
person stands on it?
2 Mechanical Equilibrium
2.3 Support Force
think!
What is the net force on a bathroom scale when a 110-pound
person stands on it?
Answer: Zero–the scale is at rest. The scale reads the
support force, not the net force.
2 Mechanical Equilibrium
2.3 Support Force
think!
Suppose you stand on two bathroom scales with your weight
evenly distributed between the two scales. What is the reading
on each of the scales? What happens when you stand with
more of your weight on one foot than the other?
2 Mechanical Equilibrium
2.3 Support Force
For an object at rest on a horizontal surface,
what is the support force equal to?
2 Mechanical Equilibrium
2.3 Support Force
think!
Suppose you stand on two bathroom scales with your weight
evenly distributed between the two scales. What is the reading
on each of the scales? What happens when you stand with
more of your weight on one foot than the other?
Answer: In the first case, the reading on each scale is half
your weight. In the second case, if you lean more on one
scale than the other, more than half your weight will be read
on that scale but less than half on the other. The total support
force adds up to your weight.
2 Mechanical Equilibrium
2.4 Equilibrium for Moving Objects
How are static and dynamic
equilibrium different?
2 Mechanical Equilibrium
2.4 Equilibrium for Moving Objects
Objects at rest are said to be in static equilibrium;
objects moving at constant speed in a straight-line
path are said to be in dynamic equilibrium.
2 Mechanical Equilibrium
2.4 Equilibrium for Moving Objects
The state of rest is only one form of equilibrium.
An object moving at constant speed in a straight-line path is
also in a state of equilibrium. Once in motion, if there is no net
force to change the state of motion, it is in equilibrium.
2 Mechanical Equilibrium
2.4 Equilibrium for Moving Objects
An object under the influence of only one force cannot
be in equilibrium.
Only when there is no force at all, or when two or more
forces combine to zero, can an object be in equilibrium.
2 Mechanical Equilibrium
Question of the Day
• Which runner is moving at a constant
speed, the forces are in equilibrium, and
the sum of the net force = 0? Explain..
2 Mechanical Equilibrium
Question of the Day-Solution
• Which runner is moving at a constant speed, the forces
are in equilibrium, and the sum of the net force = 0?
Explain..
• Runner 2, because the intervals are spaced apart the
same, and the vectors have equal length.
2 Mechanical Equilibrium
2.4 Equilibrium for Moving Objects
When the push on the
desk is the same as the
force of friction between
the desk and the floor,
the net force is zero
and the desk slides at
an unchanging speed.
2 Mechanical Equilibrium
2.4 Equilibrium for Moving Objects
If the desk moves steadily at constant speed, without change
in its motion, it is in equilibrium.
• Friction is a contact force between objects that slide or
tend to slide against each other.
• In this case, F = 0 means that the force of friction is
equal in magnitude and opposite in direction to the
pushing force.
2 Mechanical Equilibrium
2.4 Equilibrium for Moving Objects
think!
An airplane flies horizontally at constant speed in a straightline direction. Its state of motion is unchanging. In other
words, it is in equilibrium. Two horizontal forces act on the
plane. One is the thrust of the propeller that pulls it forward.
The other is the force of air resistance (air friction) that acts in
the opposite direction. Which force is greater?
2 Mechanical Equilibrium
2.4 Equilibrium for Moving Objects
think!
An airplane flies horizontally at constant speed in a straightline direction. Its state of motion is unchanging. In other
words, it is in equilibrium. Two horizontal forces act on the
plane. One is the thrust of the propeller that pulls it forward.
The other is the force of air resistance (air friction) that acts in
the opposite direction. Which force is greater?
Answer: Neither, for both forces have the same strength. Call
the thrust positive. Then the air resistance is negative. Since
the plane is in equilibrium, the two forces combine to equal
zero.
2 Mechanical Equilibrium
Question of the day
• Which geometric shape would be the
strongest? Explain
2 Mechanical Equilibrium
Solution
• Which geometric shape would be the
strongest? Explain
•Box B, because of the triangle shapes built into
the structure.
2 Mechanical Equilibrium
ILT
• What is the difference between
compression and tension.
• Demonstrate how materials move, push
together and pull apart, when you push on
them with your hand with an external
force.
2 Mechanical Equilibrium
Objective: 9/25/13
• Complete foundation:
• I will Choose one of the truss designs from the
packet and begin copying it using toothpicks.
• Begin designing and building your own blueprint
with dimensions included. Side, end, and top
views.
2 Mechanical Equilibrium
Objective: 5/3/12
• I will be able to make a structure from a
blue print.
• I will Choose one of the truss designs from
the packet and begin copying it using
toothpicks.
2 Mechanical Equilibrium
Bridge terms
• Compression: When forces squeeze
objects together, the forces cause
materials to push together.
• Tension: When forces squeeze objects
together, and the force causes materials to
stretch apart.
2 Mechanical Equilibrium
ILT: 5/8/12
• What is the length of your bridge both on
the blue print and build?
• How will you show the length on your
blueprint?
2 Mechanical Equilibrium
2.5 Vectors
To find the resultant of two vectors, construct a
parallelogram wherein the two vectors are
adjacent sides. The diagonal of the
parallelogram shows the resultant.
2 Mechanical Equilibrium
2.5 Vectors
The sum of two or more vectors is called their resultant.
Combining vectors is quite simple when they are parallel:
• If they are in the same direction, they add.
• If they are in opposite directions, they subtract.
2 Mechanical Equilibrium
2.5 Vectors
a. The tension in the rope
is 300 N, equal to
Nellie’s weight.
2 Mechanical Equilibrium
2.5 Vectors
a. The tension in the rope
is 300 N, equal to
Nellie’s weight.
b. The tension in each rope
is now 150 N, half of
Nellie’s weight. In each
case, F = 0.
2 Mechanical Equilibrium
2.5 Vectors
The Parallelogram Rule
To find the resultant of nonparallel vectors, we use the
parallelogram rule.
Consider two vectors at right angles to each other, as shown
below. The constructed parallelogram in this special case is a
rectangle. The diagonal is the resultant R.
2 Mechanical Equilibrium
2.5 Vectors
The Parallelogram Rule
In the special case of two perpendicular vectors that are equal
in magnitude, the parallelogram is a square.
The resultant is times one of the vectors.
For example, the resultant of two equal vectors of magnitude
100 acting at a right angle to each other is 141.4.
2 Mechanical Equilibrium
2.5 Vectors
Applying the Parallelogram Rule
When Nellie is suspended at
rest from the two non-vertical
ropes, is the rope tension
greater or less than the
tension in two vertical ropes?
You need to use the
parallelogram rule to
determine the tension.
2 Mechanical Equilibrium
2.5 Vectors
Applying the Parallelogram Rule
Notice how the tension vectors form a parallelogram in which
the resultant R is vertical.
2 Mechanical Equilibrium
2.5 Vectors
Applying the Parallelogram Rule
Nellie’s weight is shown by the downward vertical vector.
An equal and opposite vector is needed for equilibrium, shown by the dashed
vector. Note that the dashed vector is the diagonal of the parallelogram defined by
the dotted lines.
Using the parallelogram rule, we find that the tension in each rope is more than half
her weight.
2 Mechanical Equilibrium
2.5 Vectors
Applying the Parallelogram Rule
As the angle between the ropes increases, tension increases so that the
resultant (dashed-line vector) remains at 300 N upward, which is required
to support 300-N Nellie.
2 Mechanical Equilibrium
2.5 Vectors
Applying the Parallelogram Rule
When the ropes supporting Nellie are at different angles to the vertical, the
tensions in the two ropes are unequal.
By the parallelogram rule, we see that the right rope bears most of the load
and has the greater tension.
2 Mechanical Equilibrium
2.5 Vectors
Applying the Parallelogram Rule
You can safely hang from a clothesline hanging vertically, but
you will break the clothesline if it is strung horizontally.
2 Mechanical Equilibrium
2.5 Vectors
think!
Two sets of swings
are shown at right.
If the children on the
swings are of equal
weights, the ropes of
which swing are more likely to break?
2 Mechanical Equilibrium
2.5 Vectors
think!
Two sets of swings
are shown at right.
If the children on the
swings are of equal
weights, the ropes of
which swing are more likely to break?
Answer: The tension is greater in the ropes hanging at an
angle. The angled ropes are more likely to break than the
vertical ropes.
2 Mechanical Equilibrium
2.5 Vectors
think!
Consider what would happen if you suspended a 10-N object
midway along a very tight, horizontally stretched guitar string.
Is it possible for the string to remain horizontal without a slight
sag at the point of suspension?
2 Mechanical Equilibrium
2.5 Vectors
think!
Consider what would happen if you suspended a 10-N object
midway along a very tight, horizontally stretched guitar string.
Is it possible for the string to remain horizontal without a slight
sag at the point of suspension?
Answer: No way! If the 10-N load is to hang in equilibrium,
there must be a supporting 10-N upward resultant. The
tension in each half of the guitar string must form a
parallelogram with a vertically upward 10-N resultant.
2 Mechanical Equilibrium
2.5 Vectors
How can you find the resultant of
two vectors?
2 Mechanical Equilibrium
Assessment Questions
1.
When you hold a rock in your hand at rest,
the forces on the rock
a. are mainly due to gravity.
b. are mainly due to the upward push of
your hand.
c. cancel to zero.
d. don’t act unless the rock is dropped.
2 Mechanical Equilibrium
Assessment Questions
1.
When you hold a rock in your hand at rest,
the forces on the rock
a. are mainly due to gravity.
b. are mainly due to the upward push of
your hand.
c. cancel to zero.
d. don’t act unless the rock is dropped.
Answer: C
2 Mechanical Equilibrium
Assessment Questions
2.
Burl and Paul have combined weights of 1300 N. The tensions in
the supporting ropes that support the scaffold they stand on add to
1700 N. The weight of the scaffold itself must be
a.
b.
c.
d.
400 N.
500 N.
600 N.
3000 N.
2 Mechanical Equilibrium
Assessment Questions
2.
Burl and Paul have combined weights of 1300 N. The tensions in
the supporting ropes that support the scaffold they stand on add to
1700 N. The weight of the scaffold itself must be
a.
b.
c.
d.
Answer: A
400 N.
500 N.
600 N.
3000 N.
2 Mechanical Equilibrium
Assessment Questions
3.
Harry gives his little sister a piggyback ride. Harry weighs 400 N and
his little sister weighs 200 N. The support force supplied by the floor
must be
a. 200 N.
b. 400 N.
c. 600 N.
d. more than 600 N.
2 Mechanical Equilibrium
Assessment Questions
3.
Harry gives his little sister a piggyback ride. Harry weighs 400 N and
his little sister weighs 200 N. The support force supplied by the floor
must be
a. 200 N.
b. 400 N.
c. 600 N.
d. more than 600 N.
Answer: C
2 Mechanical Equilibrium
Assessment Questions
4.
When a desk is horizontally pushed across a floor at a steady speed
in a straight-line direction, the amount of friction acting on the desk is
a. less than the pushing force.
b. equal to the pushing force.
c. greater than the pushing force.
d. dependent on the speed of the sliding crate.
2 Mechanical Equilibrium
Assessment Questions
4.
When a desk is horizontally pushed across a floor at a steady speed
in a straight-line direction, the amount of friction acting on the desk is
a. less than the pushing force.
b. equal to the pushing force.
c. greater than the pushing force.
d. dependent on the speed of the sliding crate.
Answer: B
2 Mechanical Equilibrium
Assessment Questions
5.
When Nellie hangs at rest by a pair of ropes, the tensions in the
ropes
a. always equal her weight.
b. always equal half her weight.
c. depend on the angle of the ropes to the vertical.
d. are twice her weight.
2 Mechanical Equilibrium
Assessment Questions
5.
When Nellie hangs at rest by a pair of ropes, the tensions in the
ropes
a. always equal her weight.
b. always equal half her weight.
c. depend on the angle of the ropes to the vertical.
d. are twice her weight.
Answer: C