# Chapter 2

T = 500 N
A different scaffold that weighs 400 N supports two painters, one 500 N and the other 400 N. The reading in the left scale is 800 N.

What is the reading in the right-hand scale?

a) An object in mechanical equilibrium experiences a zero net force.
What does it mean to say something is in mechanical equilibrium?

a) An object in mechanical equilibrium experiences a zero net force.
b) An object in mechanical equilibrium is always in motion.
c) An object in mechanical equilibrium must experience no forces.
d) An object in mechanical equilibrium experiences a net force twice its weight.

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200 N
If you pull horizontally on a crate with a force of 200 N, it slides across the floor in dynamic equilibrium. How much friction is acting on the crate?
in your hand
If while riding in a smooth-riding train, you toss a coin upward, the coin will normally land ______.
W1,W2 = 417, 833 N
Henry Heavyweight weighs 1250 N and stands on a pair of bathroom scales so that one scale reads twice as much as the other.

What are the scale readings?

The coin lands off to the side of you.
If you toss a coin straight upward while riding in a train, where does the coin land when the train is rounding a corner?
It is because some force is acting upon it.
A ball rolling along a floor doesn’t continue rolling indefinitely. Is it because it is seeking a place of rest or because some force is acting upon it?
friction
If the latter, identify the force.
0 N
Two people each pull with 300 N on a rope in a tug of war. What is the net force on the rope?
300 N
How much force is exerted on each person by the rope?
W = 640 N
Lucy Lightfoot stands with one foot on one bathroom scale and her other foot on a second bathroom scale. Each scale reads 320 N .

What is Lucy’s weight?

Force can be expressed in newtons or pounds.
What are the units for force?
c) The resultant is a force of 1.41 pounds in a direction bisecting the 90-degree angle between the two vectors.
What is the resultant of a pair of one pound forces at right angles to each other?

a) The resultant is a force of 1.0 pound in a direction bisecting the angle between the two vectors.
b) The resultant is a force of 2.0 pounds in a direction bisecting the angle between the two vectors.
c) The resultant is a force of 1.41 pounds in a direction bisecting the 90-degree angle between the two vectors.
d) The resultant is zero force.

normal
A force of gravity pulls downward on a book on a table. What force prevents the book from accelerating downward?
b) In the absence of a retarding force, a body will keep moving at a constant speed in a straight line forever.
What did Galileo discover about moving bodies and force in his experiments with inclined planes?

a) Bodies rolling down an inclined plane slowed down.
b) In the absence of a retarding force, a body will keep moving at a constant speed in a straight line forever.
c) Bodies rolling down a steep inclined plane starting at a given height rolled up a gently inclined plane to a higher height.
d) Bodies rolling up an inclined plane sped up.

a) The vectors are equal in magnitude, and are opposite in direction.
What can you correctly say about a pair of vectors that add together to equal zero?

a) The vectors are equal in magnitude, and are opposite in direction.
b) The vectors are equal in magnitude, and have the same direction.
c) The vectors are not equal in magnitude, and are opposite in direction.
d) The vectors are not equal in magnitude, and have the same direction.

They have inertia−the tendency of an object at rest to stay at rest.
Why do the alphabet letters tend to do what they do when you rotate the bowl?
the upward support force
Which varies: the upward support force or the force of gravity on you?
equilibrium; support
Only when you are in __________, the _________ force exerted on you by the bathroom scale will correctly show your weight.
a) a non-zero net force
Newton said that something was needed to change the motion of an object. A clear reading of his first law tells us that what is needed is ______.

a) a non-zero net force
b) a net force
c) a force
d) no force at all

c) equal to
Recall the portion of the video in which the girl pushes her brother on the sled at constant velocity. The pushing force she exerts on the sled is _____ the frictional force the ground exerts on the sled.

a) less than
b) greater than
c) equal to

d) have constant velocity
According to Newton’s first law, when the net force acting on an object is zero, the object must _____.

a) be speeding up
b) be slowing down
c) have zero velocity
d) have constant velocity

c) be zero
An elevator moves straight upward at a constant speed. Newton’s first law predicts that the net force acting on the elevator will _____.

a) point upward
b) be increasing
c) be zero

a) when you hold the ball still in your hands before it is thrown
b) when you hold the ball still in your hands after catching it
Imagine holding a basketball in both hands, throwing it straight up as high as you can, and then catching it when it falls. At which points in time does a zero net force act on the ball? Ignore air resistance.

a) when you hold the ball still in your hands before it is thrown
b) when you hold the ball still in your hands after catching it
c) at the instant the falling ball hits your hands
d) just after the ball first leaves your hands
e) at the instant the ball reaches its highest point

800 N
If the strong man exerts a downward force of 800 N on the rope, how much upward force is exerted on the block?
No
Are there any quantities of the following, which are neither vector quantities nor scalar quantities: force, age, acceleration, temperature?
scalar quantities
age, temperature:
vector quantities
acceleration, force:
b) Zero
What is the net force on a crate sliding at an unchanging speed when pushed with a steady force of 75 N?

a) Somewhat less than 75 N
b) Zero
c) 75 N
d) Slightly more than 75 N

a) momentum
c) velocity
e) force
g) acceleration
h) displacement
Which of the following is a vector quantity?

a) momentum
b) speed
c) velocity
d) temperature
e) force
f) time
g) acceleration
h) displacement

a) pointing in the same direction
The sum of two vectors is the largest when the two vectors are _____.

a) pointing in the same direction
b) pointing in opposite directions
c) perpendicular to each other
d) positioned at a 45° angle

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