PHY 101 MIDTERM

The sketch shows a painter's scaffold in mechanical equilibrium. The person in the middle weighs 500 N, and the tensions in each rope are 400 N. What is the weight of the scaffold?

300 N

When you stretch a rubber band with a pair of fingers, what is the number of forces that should be used to described the action of your hand on the rubber band? Select the number and the associated explanation. Ignore the weight of the band.

Two forces. One pulling at each end of the band.

Some alphabet letters are floating in a bowl of soup. You want to move a letter that is far away from you closer to you. How could you rotate the bowl to do that?

Unfortunately, neither rotating the bowl clockwise nor rotating it counterclockwise will work

In daily life, people are often praised for maintaining some particular point of view, for the "courage of their convictions." A change of mind is seen as a sign of weakness. How is this different in science?

When a scientist finds evidence that contradicts a law, then the law must be abandoned.

How is the first law demonstrated in the experiment?

When no push is applied and no friction is present, the net force is zero and the object continues moving with constant velocity.

Stand next to a wall that travels at 30 km/s relative to the Sun. With your feet on the ground, you also travel at the same 30 km/s. Do you maintain this speed when your feet leave the ground? What concept supports your answer?

When you jump, you continue to move at 30 km/s due to your inertia.

As you read this in your chair, how fast are you moving relative to the chair? Relative to the Sun?

You are not moving relative to the chair, but you are moving over 100,000 km/h relative to the Sun

What did Galileo discover about moving bodies and force in his experiments with inclined planes?

In the absence of a retarding force, a body will keep moving at a constant speed in a straight line forever.

What kind of speed is registered by an automobile speedometer?

Instantaneous speed

What type of path does a moving object follow in the absence of a force?

It continues to move in a straight line at a constant speed

How does the distance traveled by the ball in the second half second compare with the distance traveled by the ball in the first half second?

It increases.

If a car is moving at 90 km/h and it rounds a corner, also at 90 km/h, does it maintain a constant speed? A constant velocity?

It maintains a constant speed, but does not maintain a constant velocity.

In the setup suggested in the procedure, the projection surface is perpendicular to the direction of incidence of the light. Consider the case where the surface is not perpendicular but, rather, is tilted with respect to the direction of incidence of the light. What is the main effect of the tilting on the observed illuminated area?

It makes the shape of the area elliptical instead of circular.

Why are students of the arts encouraged to learn about science and science students encouraged to learn about the arts?

Knowing both the arts and sciences makes for a wholeness in the way we view the world

The weights of Burl, Paul, and the scaffold produce tensions in the supporting ropes. Rank the tension in the left rope, from most to least, in the three situations, A, B, and C.

Most: closest Least: furthest

What determines the shape of the illuminated region?

Mostly, it is determined by the shape of the object (the Sun or the lamp).

You pull one rubber band with one finger from each hand until it shows 2 units of deformation. Which of the following combinations of rubber bands produce the same force experience on your fingers?

Pulling two rubber bands at the same time so that they reach 1 unit of deformation.

If you push on a crate with a horizontal force of 100 N and it slides at constant velocity, what is the magnitude and direction of the frictional force acting on the crate?

The frictional force on the crate is 100 N opposite the direction of motion.

A sheet of paper is dropped from a height of 2 meters. As it passes by a point at a height of 1 meter, an identical sheet of paper is released from that height. Which one gets to the ground first? Select the best answer and reasoning.

The sheet dropped from 2 meters reaches the ground first. It has a non-zero speed as it reaches the 1 meter height while the speed of the second object is zero. Later, the first sheet always has a larger speed than the second.

The experiment does not directly measures the relation between time and distance but we know that these are related by the equation y=(1/2)gt2 where y is the distance fallen, g is the free fall acceleration (you can take as 10 m/s2), and t is the time. Determine the time it takes for an object to fall 2 meters.

0.63 s.

Acceleration is a vector and has direction. When the object moves to the right and speeds up, what is the direction of the acceleration?

To the right

Select the correct equations that show that the average speed of a rabbit that runs a distance of 26 m in a time of 2 s is 13 m/s .

v=s/t= (26m)/(2s)= 13m/s

State the equilibrium rule for forces in symbolic notation

ΣF = 0

What is the distance between Earth to the Sun measured in Sun diameters? Answers are rounded up to one significant digit.

100 Sun diameters

What is the speed over the ground of an airplane flying at 100 km/h relative to the air caught in a 100-km/h right-angle crosswind?

141 km/h

In the experiment you observed and measured the lengths of the band under different forces. Which of the following sets of measures of length, for forces (weights) of magnitude 0, 1, 2, 3, would more likely correspond to an actual band? In each answer the list is the set of lengths in cm. of the band. Remember that it was noted that the bands are not likely to obey a perfect Hook law.

15, 17, 20, 23, 26.

Assume that the lamp used in the experiment emits light from a surface of diameter 10 cm and that is located at 1 m. from the pinhole. If the pinhole is 0.5m from the projection surface, what is the diameter of the illuminated region?

5 cm.

The experiment does not directly measures the relation between time and distance but we know that these are related by the equation y=(1/2)gt2 where y is the distance fallen, g is the free fall acceleration (you can take as 10 m/s2), and t is the time. Determine the distance fallen, in meters, after 1 second.

5.0 m.

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?

500 N

Three pucks, A, B, and C, are shown sliding across ice at the noted speeds. Air and ice friction forces are negligible. Rank them, from greatest to least, by the force needed to stop them in the same time interval.

6, 4, 2

Lucy Lightfoot stands with one foot on one bathroom scale and her other foot on a second bathroom scale. Each scale reads 330 N. What is Lucy's weight?

660 N

Why do we say that force is a vector quantity?

A force has a magnitude and a direction.

Select a correct description of what a force is along with a correct statement of their properties.

A force is a pull or a push on an object that can be described as a vector.

What is the test for whether a hypothesis is scientific or not?

A hypothesis is scientific if it is possible to prove it wrong

In daily life, we see many cases of people who are caught misrepresenting things and who soon thereafter are excused and accepted by their contemporaries. How is this different in science?

A scientist who lies in a scientific publication will suffer professional excommunication.

Consider the video demonstration that you just watched. Which of the following changes could potentially allow the ball on the straight inclined (yellow) track to win? Ignore air resistance.

A. Increase the tilt of the yellow track

In the figure below, label the essential components used to triangulate the distance to the tree located on the opposite side of the river (assume the baseline remains constant).

A: angle that decreases with increasing distance to the object.....E: Angle that increases with increasing distance to object....D: Baseline....C: Right angle....B: Distance to object

When the same push is applied to an object of different mass, several aspects of the motion change. Which is the key change?

After mass change the acceleration is different.

Three pucks, A, B, and C, are shown sliding across ice at the noted speeds. Air and ice friction forces are negligible. Rank them, from greatest to least, by the force needed to keep them moving.

All equal

What is science:

All of the above

What does it mean to say something is in mechanical equilibrium?

An object in mechanical equilibrium experiences a zero net force.

Free fall is a form of accelerated motion. What does this mean for a falling object?

As time increases, the distance travelled in the same time interval increases.

When Dr. Hewitt drops a book and a crumpled piece of paper together from the same height, which object hits the ground first, and why?

Both objects hit the ground at the same time because air resistance is negligible.

Which of the following are scientific hypotheses?

Chlorophyll makes grass green. Tides are caused by the Moon.

What two units of measurement are necessary for describing speed?

Distance and time

What is the role of equations in this book?

Equations are guides to thinking and show connections between concepts.

In the classic experiment that you have repeated, two objects of different mass are dropped from the same elevation. If drag is not an important factor the two objects fall to the ground at the same time. From the point of view of Newton's second law, what is the reason for this?

For a larger mass the gravitational force is larger but its inertia (its mass) is also larger. Their ratio is the same for all objects and therefore the acceleration and motion are equal.

What are the units for force?

Force can be expressed in newtons or pounds.

What relationship between distance traveled and time did Galileo discover for freely falling objects released from rest?

Galileo discovered that distance increased as the time squared.

What did Galileo discover in his legendary experiment on the Leaning Tower of Pisa?

Galileo found that a heavier stone does not fall significantly faster than a lighter one.

Why does the distance traveled by the ball in each half second after it is released change in the way in which it does?

Gravity is pulling down on the ball, so it accelerates down at a steady rate.

A stubborn stump is pulled by a pair of ropes, each with a force of 200 N, but at different angles as shown.

Greatest: smaller angle Least: largest angle

Must people choose between science and religion?

No, there is no contradiction in being scientific and religious in one's thinking

When you hang one reference object from a rubber band you obtain one unit of deformation. Consider the case where you hang this system from another rubber band, so that you have two rubber bands, vertical, one after another. What is the deformation of the bands? Ignore the weight of the bands. You are still only using one reference object.

One unit of deformation in both of the bands.

Clearly distinguish between science and technology.

Science gathers the knowledge that technology uses for practical purposes.

What test can you perform to increase the chance in your own mind that you are right about a particular idea?

See if you can state the objections of your opponents to their satisfaction

Heliocentric:

Sun Centered, orbital speeds

According to the parallelogram rule, what quantity is represented by the diagonal of a constructed parallelogram?

The diagonal is the resultant, or sum, of two vectors.

Listed following are a series of statements that each make a claim. Classify these as either testable by accepted methods of science or non-testable by accepted methods of science. Be sure to note that this question does not ask whether a statement would pass or fail a test; it only asks whether it is testable in principle.

Testable: Bacteria, Earth orbits, People, mars, solar eclipse..........Not testable: Vince, Hurricane Katrina

The force of gravity, just as all forces, is an action on an object. Forces appear due to the interactions between pairs of objects. Therefore, for the force of gravity to act on a falling object, there should be another object that, in a sense, is creating that force. Which object is responsible for creating the force of gravity observed on falling objects?

The Earth as a whole.

When the Sun was directly overhead in Syene, why wasn't it directly overhead in Alexandria?

The Earth is a sphere.

Why did Aristarchus choose the time of a half Moon to make his measurements for calculating the Earth -Sun distance?

The Earth, Moon, and Sun formed a right triangle at that time

How does the Moon's diameter compare with the distance between Earth and the Moon?

The Moon's diameter is 1/110 the distance between Earth and the Moon.

Earth, like everything else illuminated by the Sun, casts a shadow. Why does this shadow taper?

The Sun is much larger than the Earth

Based on the experiment that Dr. Hewitt demonstrated in the video, what factors determine whether the air resistance experienced by a falling object will affect the motion of the object?

The area of the object in relation to the weight of the object determines the air resistance the object experiences. Objects having greater area but smaller weight experience greater effect of air resistance.

The drag on an object depends on several variables. The most important of them, to understand the experiments you carried out is:

The area of the object.

You drop two pieces of paper. The first is a full sheet of paper that is left flat, the second is half the size of the first but is crumpled into a tight ball. Which one reaches the ground first. Select the best answer and reasoning.

The ball reaches the ground first. It does not experience a significant drag, compared to the flat sheet.

Dr. Hewitt has clay "blobs" hanging on either side of his head in this video. When he turns around, what happens to the blobs?

The blobs tend to stay where they were.

In the video, Dr. Hewitt drops a book and a flat piece of paper together from the same height. Which object that hits the ground first?

The book hits the ground first.

For the determination of the size of the sun, the experiment requires a piece of information that is not directly measured. This is:

The distance from Earth to Sun

Which is more likely to break: a hammock stretched tightly between a pair of trees or one that sags more when you sit on it?

The hammock stretched tightly between a pair of trees is more likely to break.

In the video, Dr. Hewitt drops a book and a flat piece of paper together from the same height, and one object hits the ground before the other. Why does that object hit the ground first?

The heavier object--the book--hits the ground first because the other, lighter, object is more influenced by air resistance.

Which quantity cannot be determined from the experiment?

The mass of the Sun

In the experiment you used objects with masses that were not necessarily known. Assume that for a certain object you observed a deformation of size 3. Next, you remove that object and hang a second, different object, made of different materials, and observe that the deformation is the same. What can you say about the mass of the second object compared to the first? Select, the correct answer and the best argument for it.

The masses are equal. Objects of equal mass have the same weight, which is the force producing the deformation.

What is the net force on a bag pulled down by gravity with a force of 18 newtons and pulled upward by a rope with a force of 18 newtons?

The net force is zero newtons.

What is the net force on an object in either static or dynamic equilibrium?

The net force is zero.

A rubber band is used to hold an object. What is the net force on the rubber band? Select the best answer.

The net force is zero. The sum of forces on the rubber band cancel.

What is the definition of the net force?

The vector sum of the forces on an object.

What can you correctly say about a pair of vectors that add together to equal zero?

The vectors are equal in magnitude, and are opposite in direction

When Dr. Hewitt pulls the tablecloth, why do the items on the tablecloth do what they do?

Their inertia is sufficient to keep them there.

What are the circular spots of light seen on the ground beneath a tree on a sunny day?

These are pinhole images of the Sun

When Dr. Hewitt drops a book and a crumpled piece of paper together from the same height, which one hits the ground first?

They both hit the ground at the same time.

Why do the alphabet letters tend to do what they do when you rotate the bowl?

They have inertia−the tendency of an object at rest to stay at rest.

Why do the clay blobs do what they do when Dr. Hewitt turns around?

They have inertia−the tendency of an object at rest to stay at rest.

When Dr. Hewitt pulls the tablecloth, what happens to the items on the tablecloth?

They tend to stay where they were.

Similar to the case in the experiment you use two rubber bands, side to side first, to hold a weight of 3 reference objects. Then, as in the experiment, the bands are pulled apart in their free ends until they form an angle of 30 degrees with respect to the horizontal. What are the deformations observed in these bands?

Three units of deformation.

You tell your friend about the neat tablecloth trick that Dr. Hewitt demonstrated. Your friend tries to repeat this trick at home and later complains to you that it failed. Which of the following is most likely the reason that it failed?

Your friend pulled the tablecloth too slowly.

When you stand at rest on a bathroom scale, how does your weight compare with the support force from the scale?

Your weight is equal in magnitude and opposite in direction to the support force from the scale.

A theory in the field of science is:

a synthesis of a large body of well-tested knowledge.

Select the correct equations that show that the acceleration of a hamster is 5 m/s^2 when it increases its velocity from rest to 10 m/s in 2 s.

a=Δv/t=(10m/s)/(2s)=5m/s^2

Eratosthenes' measurements of Earth's size involved:

all of the above

How can you use the graph of velocity versus time to estimate the acceleration of the ball?

by estimating the value of the slope of the graph

Geo centric:

earth centered, epicycles

Pseudoscience is best characterized as being:

fake.

An educated scientific guess is a:

hypothesis.

Is the tension in the rope less than, equal to, or greater than 50 N?

less

both:

planetary motion, brightness, uniform motion

A force of gravity pulls downward on a book on a table. What force prevents the book from accelerating downward?

support