ELED 303: Exam 1 (physics)

Which of the following represents Newton's Second Law of Motion?

(Net force acting on an object) = (mass of the object)(acceleration of the object)

A car moves with a forward thrust of 200 Newtons against a backward friction-drag of 100 Newtons. The car pulls a load of 20 kilograms. If you ignore the mass of the car and its driver, what is the net force on the car? (QUESTION 4)

100 Newtons

I push my kids in the stroller with a force of 100 Newtons on a frictionless surface like ice. The stroller and kids have an approximate mass of 50 kilograms. Assuming I can actually move on ice, what is the resulting acceleration of the stroller?

2 meters per second squared

If a car travels at an average speed of 60km/h for an hour, it will cover a distance of 60km. How far would it travel if it moved at this rate for 4h?

240 km

What is the average speed of a cheetah that sprints 100m in 4s?

25 m/s

Same scenario as qustion #4 --- If you ignore the mass of the car and its driver, what is the acceleration of the car?

5 meters/second for every second of travel

If a camel can travel at an average velocity of 32km per hour, how far has it traveled after 3 hours?

96 km

In which of the following examples is the motion of the car NOT accelerated?

A car climbs a steep hill at a constant speed

In which of the following examples is the motion of the car accelerated?

A car climbs a steep hill with its speed dropping from 18 km/h at the bottom to 9 km/h at the top.

Vector

A quantity that has both magnitude and direction. Force, velocity, and acceleration are all vectors. You can add and subtract vectors, multiply them in various ways, and even use them to describe how subatomic particles behave.

Acceleration

Any change in motion of an object. A change in direction and/or speed. Accelerations are caused by net forces. Acceleration is a vector.

Complete the following statement: Newton's first law states that every object continues in a state of rest, or in a a state of motion in a straight line at a _________ speed, unless it is compelled to change that state by an unbalanced force.

Constant

Select the FALSE statement regarding net force. For help on this question, check out this section of the Science Object again.

Direction of the forces is NOT important when determining net force

According to Newton's second law, if you double the unbalanced force on an object of a given mass the acceleration will be . . . Hint: Think about adding an extra power booster to increase the thrust of a rocket, how will acceleration be affected? Or think about me pushing my 3yo Nolan in the stroller twice as hard . . . What will happen to acceleration? In these situations, mass is not changing.

Doubled

If a force is exerted on an object, you can be sure the object will accelerate.

False. In order to figure out whether or not an object will accelerate, you must determine the net force acting on it. It's possible that the force in question is balanced out by another force, leading to zero net force and zero acceleration.

Mass is a measure of how hard something pushes back on you when you try and exert a force on it.

False. Mass is a measure of an object's inertia. As such, the number associated with mass tells you how difficult it is to change the object's motion. You can use the value of the mass in F=ma to determine what acceleration will result from a given net force.

Newton's Third Law

For every action there is an equal and opposite reaction

In physics, what term describes a "push, pull, hit, or shove"?

Force

Newton's Second Law

Force equals mass times acceleration

1 / 1 point Does the speedometer on a vehicle show average speed or instantaneous speed?

Instantaneous speed

What are scientifically correct methods one can use to specify the position of an object?

Longitude and latitude x and y coordinates on a grid

Which one of the following is a measure of inertia?

Mass

Select the best answer.

Mass is a measure of inertia. Weight is affected by gravity. The reluctance of an object to change its state of rest or of uniform motion in a straight line is called inertia. All of the above are true.

In the Science Object, you watched an animation in which a tortoise won a race against a hare. Which one of the animals had a constant velocity?

Neither the tortoise or hare

You are driving from Sioux Falls to Rapid City on the interstate. Your vehicle is moving directly west at a constant speed of 75 miles per hour, and has a mass of 1500kg.

Net force on the car is zero (IS THE CAR ACCELERATING- NO)

Netwon's First Law of Motion

Newton's First Law of Motion states, "An object at rest remains at rest and an object in motion remains in motion at a constant speed in a straight line unless acted upon by an unbalanced force"

What part of Newton's First Law does the coin in the "coin trick" video illustrate?

Objects at rest tend to remain at rest

What are the two parts of Newton's First Law of Motion? Select all that apply.

Objects at rest tend to remain at rest unless acted on by an unbalanced force Objects in motion tend to stay in motion in a straight line unless acted on by an unbalanced force

What part of Newton's First Law does Wiley the Coyote illustrate in the cartoon? (Coyote running, gets to the end of the cliff...then what?)

Objects that are moving tend to keep moving

The rate at which an object travels a certain distance is known as

Speed

I have four children; their ages are 10yo, 3yo, 2yo, and 5 months. Our house is kind of CRAZY - our 3yo Nolan is shown below. To help transport all of these children when we leave the house, we have a double stroller. Which of the following scenario's will produce the greatest acceleration of the stroller if I push my kids with the same force?

The 5 month old baby is the only passenger

Which of the following statements are TRUE regarding the "coin trick"?

The NSTA card moves from a state of rest because a person exerts an unbalanced force on it

A net, unbalanced force acting on an object will always cause the object to accelerate. That acceleration will always show up as a change in speed.

The first part of this statement is true. Net forces cause objects to accelerate. The second sentence is false. The object's acceleration might show up as a change in speed, but it could also show up as a change in direction.

While driving down the highway, a mosquito is squashed on your wind shied of your car. Think about carefully about Newton's 3rd Law. Select all that apply.

The force of the mosquito on the windshield is equal in magnitude to the force of the car on the mosquito The acceleration of the mosquito is greater than the acceleration of the car (if the car is accelerating at all) even though the same force is applied to both the mosquito and car

1 / 1 point Which of the following describes Newton's Third Law of Motion?

The law explains the conditions under which an object's motion will change The law explains that the natural tendency for things in the universe to stay at rest or in motion in a straight line. The law explains how forces affect changes in motion **The law explains that whenever one object exerts a force on a second object, the second object exerts a force on the first object that is equal in magnitude and acts opposite in direction

Which of the following describes Newton's Second Law of Motion?

The law explains the relationship between an object's mass, its acceleration, and the net force applied to the object

Using Newton's Third Law of Motion, what is happening in the picture? (Man leaning against a wall)

The man pushes on the wall and the wall pushes back on the man When the man pushes on the wall, the electromagnetic forces among the atoms in the wall act like a spring and push back on the man

Now thinking about Newton's Second Law . . . WHY did you select the scenario you selected in the above question?

The scenario had the least amount of inertia

Velocity

The speed and direction something is moving. Velocity is a vector.

This time I push my kids in the stroller through mud. I coninue to push my kids in the stroller with a force of 100 Newtons but encounter 25 Newtons of friction from the mud. The stroller and kids have an approximate mass of 50 kilograms. What is the resulting acceleration of the stroller?

The stroller will accelerate at 1.5 meters per second for every second of travel

Net force

The sum total of all the forces acting on an object. Direction is important, so you don't just add the numbers together. Two or more forces can cancel each other with appropriate directions.

Inertia

The tendency of a body to maintain its state of rest or uniform motion unless acted upon by an external force. The tendency of an object to keep doing whatever it's doing; an object will maintain its state of rest or uniform motion unless acted upon by an external force. The inertia of an object is measured by its mass.

Now let's consider the magnitude (or amount) of and direction of the force in the picture above. Let's say the man pushes on the wall with a force of 10 Newtons

The wall pushes back on the man with a force that is equal in magnitude to 10 Newtons but opposite in direction

Suppose you are pulling a wagon along the sidewalk. If the mass of the wagon remains the same and the acceleration of the wagon increases, that causes the force you are applying to increase.

This is sort of true and sort of false. An increase in the wagon's acceleration implies that you have increased the net force acting on it (use the teeter-totter to check this). Changing the wagon's acceleration does not, however, cause the net force to increase. Net forces cause accelerations, not the other way around.

Why do we say velocity is a vector quantity and speed is not?

Velocity describes magnitude and direction but speed describes only magnitude

What is true about Velocity?

Velocity is an example of a vector quantity. Speed is NOT an example of a vector quantity.

The speed of a car heading directly west changes from 45 miles/h to 75 miles per hour. In this example,

Velocity is changing

Fill in the blanks. ____________ describes how fast and in what direction an object is moving while acceleration describes the rate at which velocity changes over ________.

Velocity, time

Do scientists believe there are situations in which Newton's laws do not apply?

Yes, there are limits to Newton's laws At high speeds (near the speed of light), Newton's laws need some adjustment and do not apply

Galileo and Newton believed

a moving object would keep moving in a straight line forever if no outside forces acted on it

What is inertia?

a property of an object; an object's tendency to keep doing what it's doing

Let's put some ideas together from the first and second Science Objects on motion. Which of the following are examples of forces? Select all that apply.

a push friction a pull

How fast you are changing your speed, direction of travel, or both speed and direction of travel is a property of motion known as

acceleration

While a car travels north at a constant speed its

acceleration is zero

Which of the following would be examples of an object, once set in motion, remains in motion in a straight line forever without any external push to keep it moving.

an asteroid moving through space (ignore the effects of the sun's gravity on the asteroid)

Which one of the following has the greatest amount of inertia? Hint: In this question, I want you to realize that the amount of inertia that an object has does not depend on its state of motion. In other words, a mack truck has the same amount of inertia whether it is at rest or moving down the highway at 75 mph.

an elephant

A moving car has __________ inertia compared to the same car at rest. A hint: an elephant has the same amount of inertia whether it is standing still or charging at you.

an equal amount of

What is needed to accurately describe the position of an object?

both distance and direction to the object from a given point

With all other factors equal, if you double the mass of an object while a constant unbalanced force is applied, the acceleration will be . . . Hint: Now think about adding an extra rocket to an existing rocket with only one power booster, how will acceleration be affected? Or think about me trudging along in the mall with all 4 kids in tow, and my two year old Jack (who happens to weigh as much as his three year old brother Nolan) jumps in the stroller with Nolan. What will happen to acceleration? Note that in all of these situations, mass is changing but force is not

decreased by one-half

Which of the following are required to describe velocity?

distance traveled, time of travel, and direction of travel

Acceleration = change in velocity / time for the change

formula for acceleration

average speed = distance traveled/ time of travel

formula for average speed

speed = distance/time

formula for speed

If an object falls with constant downward acceleration, the speed of the object must

get bigger

Complete the following statement about Newton's first law of motion. An object at rest continues to stay at rest because it has:

inertia

Newton's first law of motion describes

inertia

Using the following list, select all units that could be used to describe speed.

m/s

Using the following list, select all units that could be used to describe acceleration.

m/s2 . m/s/s

What factors are necessary to determine a vector quantity?

magnitude and direction

From the following list, select all units that could be associated with a vector quantity.

meter/second (m/s)

Rub your hands together. This is an example of friction. What is friction?

the force or resistance encountered when one body is moved in contact with another

Aristotle believed

the natural state of objects was to be at rest on the Earth, a continuous force was needed to keep objects moving

In the Science Object, you watched an animation in which a tortoise won a race against a hare. Which one of the animals had a constant speed?

tortoise