PHY099 - Knowledge Checks

What does it mean for two quantities to be inversely proportional to each other?

When one variable increases, the other variable decrees by the same factor.

Boat A and boat B are traveling at a constant speed in opposite directions when they pass each other. Yes or no—If a person in each boat describes motion based on the boat's own reference frame, will the description by a person in boat A of boat B's motion be the same as the description by a person in boat B of boat A's motion?

Yes, both people will describe the same motion because they will perceive the other as moving in the backward direction.

The tires you choose to drive over icy roads will create more friction with the road than your summer tires. Which option is another example where more friction is desirable?

Jogging track

When a large body of experimental evidence supports a hypothesis, what may the hypothesis eventually be considered?

Law

A girl rolls a basketball across a basketball court. The ball slowly decelerates at a rate of -0.20 m/s2. If the initial velocity was 2.0 m/s and the ball rolled to a stop at 5.0 s after 12:00 p.m., at what time did she start the ball rolling?

5 s before noon

Using the graph, what is the runner's velocity from 4 to 10 s?

0 m/s

Which variable represents displacement?

d

A marathon runner completes a 42.188-km course in 2 h, 30 min, and 12 s. There is an uncertainty of 25 m in the distance traveled and an uncertainty of 1 s in the elapsed time. 1. Calculate the percent uncertainty in the distance. 2. Calculate the uncertainty in the elapsed time. 3. What is the average speed in meters per second? 4. What is the uncertainty in the average speed?

0.059%, 0.01%, 4.681 m/s, 0.003 m/s

A position vs. time graph of a frog swimming across a pond has two distinct straight-line sections. The slope of the first section is 1 m/s. The slope of the second section is 0 m/s. If each section lasts 1 s, then what is the frog's total average velocity?

0.5 m/s

A car travels with an average velocity of 23 m/s for 82 s. Which of the following could NOT have been the car's displacement?

1,900 m east

Rhianna and Logan start at the same point and walk due north. Rhianna walks with an average velocity Logan walks three times the distance in twice the time as Rhianna. Which option expresses Logan's average velocity in terms of vavg,R? Logans Average velocity = 1.5v Logans Average velocity = 2/3v Logans Average velocity = 3v Logans Average velocity = 1/2v

1.5v

An object has a mass of 1 kg on Earth. What is its weight on the moon?

1.67 N

A swimmer bounces straight up from a diving board and falls feet first into a pool. She starts with a velocity of 4.00 m/s and her takeoff point is 8 m above the pool. How long are her feet in the air?

1.75 s

A person pushes an object of mass 5.0 kg along the floor by applying a force. If the object experiences a friction force of 10 N and accelerates at 18 m/s2, what is the magnitude of the force exerted by the person?

100 N

A good-quality measuring tape can be off by 0.50 cm over a distance of 20 m. What is its percent uncertainty in scientific notation?

2.5x10^-2%

What would be the slope for a line passing through these two points? Point 1: (1, 0.1) Point 2: (7, 26.8)

4.5

A velocity vs. time graph starts at 0 m/s and ends at 10 m/s, stretching over a time-span of 15 s. What is the object's displacement?

75 m -- Select "Cannot be determined from the information given." -- The object's displacement is the area under the velocity vs. time graph. Since the graph is not shown, the object's displacement can't be determined.

Why should you specify a reference frame when describing motion?

A description of motion depends on the reference frame

A body with mass m is pushed along a horizontal surface by a force F and is opposed by a frictional force f. How would you draw a free-body diagram to represent this situation?

A dot with an arrow pointing right, labeled F, and an arrow pointing left, labeled f, that is of equal length or shorter than F.

A free-body diagram shows the forces acting on an object. How is that object represented in the diagram?

A single point

What would the velocity vs. time graph of the object whose position is shown in the graph look like?

A straight line with a positive slope -- The average velocity between points is gradually increasing, so a line with a positive slope would represent the velocity vs. time graph.

How can you use the definition of acceleration to explain the units in which acceleration is measured?

Acceleration is the rate of change of velocity. Therefore, its unit is meter per second squared (m/s^2).

What kind of motion would create a position graph like the one shown? - The graph shows increasing velocities from 0 s to 10 s, and from 10 s to 20 s. Increasing velocity is acceleration.

Any motion that accelerates

A student is asked to solve the following problem: An object falls from a height for 2.0 s, at which point it is still 60 m above the ground. What will be the velocity of the object when it hits the ground? Which option provides the correct order of kinematic equations that can be used to solve the problem?

B

Why is Einstein's theory of relativity considered part of modern physics, as opposed to classical physics?

Because it was among the new 19th century discoveries that changed physics.

Which question regarding a strain of genetically modified rice is NOT one that science can answer?

Should the genetically modified rice be grown commercially and sold in the marketplace?

Billy drops a ball from a height of 1 m. The ball bounces back to a height of 0.8 m, then bounces again to a height of 0.5 m, and bounces once more to a height of 0.2 m. Up is the positive direction. What is the total displacement of the ball and the total distance traveled by the ball?

The displacement is equal to -1 m and the distance is equal to 4 m

The graph shows velocity vs. time. Calculate the net displacement using seven different divisions. Calculate it again using two divisions: 0 → 40 s and 40 → 70 s. Compare. Using both, calculate the average velocity.

Displacement and average velocity using seven divisions are 15,500 m and 221.4 m/s while with two divisions are 14,312 m and 204.5 m/s. -- The net displacement is estimated by adding the areas of the trapezoids formed by each division. Since the curve is concave down, the area using trapezoids with seven divisions will be larger than using trapezoids with two divisions. So, the estimated net displacement will be larger with seven divisions. Since the average velocity is just the net displacement divided by 70 s, the same will be true in that case. The correct answer is the only one where both the estimated net displacements and average velocities are larger when estimated using seven divisions.

What does your car's odometer record?

Distance

What is dynamics?

Dynamics is the study of forces and their effect on motion

A steadily rolling ball is pushed in the direction from east to west, which causes the ball to move faster in the same direction. What is the direction of the acceleration?

East to west

Which forces cause the motion of a system?

External Forces

What kind of force is friction?

External force

One object exerts a force of magnitude F1 on another object and experiences a force of magnitude F2 in return. What is true for F1 and F2?

F1=F2

Imagine that a car is traveling from your left to your right at a constant velocity. Which two actions could the driver take that may be represented as (a) a velocity vector and an acceleration vector both pointing to the right and then (b) changing so the velocity vector points to the right and the acceleration vector points to the left?

For (a), push down on the accelerator and then (b) push down on the bakes.

What is a physical quantity that can be described by dynamics but not by kinematics?

Force

Which hypothesis cannot be tested experimentally?

Ghosts are the souls of people who have died.

The free-electron model of metals explains some of the important behaviors of metals by assuming the metal's electrons move freely through the metal without repelling one another. In what sense is the free-electron theory based on a model?

It involves analyzing an imaginary system simpler than the real wire it resembles.

What could you conclude about these two lines? Line A has a slope of -4.7. Line B has a slope of 12.0.

Line A is decreasing while line B is increasing, with line B being much steeper than line A.

Which statement best describes the relationship between instantaneous velocity and instantaneous speed?

Magnitude of instantaneous velocity is equal to instantaneous speed.

How is modeling useful in studying the structure of the atom?

Modeling replaces the real system with something similar but easier to examine.

Which statement best compares and contrasts the aims and topics of natural philosophy versus physics?

Natural philosophy included all aspects of nature including physics.

In the equation for Newton's second law, what does Fnet stand for?

Net external force

Yes or no—Is it possible to determine a car's instantaneous velocity from just the speedometer reading?

No, it reflects speed but not the direction.

Can one-dimensional motion have zero distance but a nonzero displacement? What about zero displacement but a nonzero distance?

One-dimensional motion cannot have zero distance with nonzero displacement. Displacement has both magnitude and direction, but it can have zero displacement with nonzero distance because distance has only magnitude and any motion will be the distance it moves.

How could physics be useful in weather prediction?

Physics helps predict dynamics and movement of weather phenomena.

Light travels as waves at an approximate speed of 300,000,000 m/s (186,000 mi/s). Designers of devices that use mirrors and lenses model the traveling light by straight lines, or light rays. Why would it be useful to model the light as rays of light instead of describing them accurately as electromagnetic waves?

Studying a model makes it easier to analyze the path that the light follows.

Which statement explains why a racecar going around a curve is accelerating, even if the speed is constant?

The car is accelerating because the direction of velocity if changing.

Which option does NOT contribute to uncertainty?

The regularities in the object being measured

A hockey puck is shot down the arena in a straight line. Assume it does not slow until it is stopped by an opposing player who sends it back in the direction it came. The players are 20 m apart and it takes 1 s for the puck to go there and back. Which option describes the graph of the displacement over time? Consider the initial direction of the puck to be positive.

The graph is a downward opening V.

Identify the time, or times, at which the instantaneous velocity is greatest, and the time, or times, at which it is negative. A sketch of velocity vs. time derived from the figure will aid in arriving at the correct answers.

The instantaneous velocity is greatest at d, and it is negative at a, b, and f. -- You can compare the tangent lines at each position along the curve. The magnitude of the slope of the tangent line is greatest at d, indicating the time when the instantaneous velocity is greatest. The slopes are negative at points a, b, and f, showing that the instantaneous velocity is negative at those points.

What is meant when a physical law is said to be universal?

The law applies everywhere in the universe.

A car is moving on a straight road at a constant speed in a single direction. Which statement is true?

The magnitude of average velocity is equal to the average speed.

Three forces, A, B, and C, are acting on the same object with magnitudes a, b, and c, respectively. Force A acts to the right, force B acts to the left, and force C acts downward. What is a necessary condition for the object to move straight down?

The magnitude of force A must be equal to the magnitude of force B, so a = b.

What is the net external force on an object in freefall on Earth if you were to neglect the effect of air?

The net force is downward with magnitude mg.

Using the graph, what is the average velocity for the whole 10 s?

The total average velocity is 1.2 m/s

In a free-body diagram, the arrows representing tension and weight have the same length but point away from one another. What does this indicate?

They are equal in magnitude and act in opposite directions.

You are characterizing the motion of an object by measuring the location of the object at discrete moments in time. What is the minimum number of data points you would need to estimate the average acceleration of the object?

Three -- Two points are needed to find the value of the average velocity over one time interval, and a third point is needed to find a value of average velocity over a second time interval. Determining two average velocities allows an estimate of average acceleration.

True or false—A book placed on a balance scale is balanced by a standard 1-kg iron weight placed on the opposite side of the balance. If these objects are taken to the moon and a similar exercise is performed, the balance is still level because gravity is uniform on the moon's surface as it is on Earth's surface.

True

True or false—A person accelerates while walking on the ground by exerting force. The ground in turn exerts force F1 on the person. F1 and F2 are equal in magnitude but act in opposite directions. The person is able to walk because the two forces act on the different systems and the net force acting on the person is nonzero.

True

True or false—A rocket is launched into space and escapes Earth's gravitational pull. It will continue to travel in a straight line until it is acted on by another force.

True

A ball is dropped and hits the floor. What is the direction of the force exerted by the floor on the ball?

Upward

For the motion of a falling object, which graphs are straight lines?

Velocity versus time and acceleration versus time