PHY 103 exam 1
Quentin, whose mass is 69 kg, is riding on a 3.5 kg skateboard initially traveling at 9.0 m/s. He drags his foot to brake the skateboard with a constant force, bringing it to a stop in 4.0 s. What force does he apply
-18.13N
Calculate the velocity of the particle during the interval, t=0.20 min and t=0.40 min.
0 km/hr
What does it mean when you say something has inertia? Give three examples that demonstrate the concept of inertia.
Inertia means resistance to change in motion of an object. Some examples that demonstrate the concept of inertia are body movement to the side when a car makes a sharp turn or doing an activity such as ice skating. Second example, when a seat belt tightens in a car when it stops quickly. Lastly, a pebble or ball rolling down a hill will continue to roll unless friction or another force stops it.
A friend tells you that a rowboat is propelled by the force of its oars against the water. First, explain whether the statement is correct, and then identify the action and reaction forces.
It is incorrect because it is the force of the water against the oars that propels the boat forward. The oars pushing against the water is the action force, and the water pushing back against the oars is the reaction force.
Why you need a force to change the motion of an object?
because they have intentional. amount of inertia depends of mass only.
When an unbalanced force acts on an object, the force
changes the motion of the object.
Displacement is distance combined with
direction
The word rate is a clue that something is being__________ time
divided by
The Earth exerts a force on a flea equal to the flea's weight, W. According to Newton's Third Law of Motion, how much force does the flea exert on the Earth?
exactly W
According to Newton's third law of motion, when a hammer strikes and exerts force on a nail, the nail
exerts an equal force back on the hammer.
A body traveling at constant speed changes its direction without a change in its velocity.
false
If you start with an initial velocity of 17 m/s and have an acceleration of , what is your final velocity after 9 seconds?
final velocity = -1m/s
Newton's second law of motion states the relationship of mass, acceleration, and force. It states that
force equals mass times acceleration
A force that resists motion created by objects rubbing together is
friction
A man is driving his car north on the highway at a constant velocity of 50 mph for 100 s. What is the value of his acceleration?
his acceleration is zero because he is driving at a constant velocity
The product of a force and the length of time the force is applied to an object is called____________and causes a change in its momentum
impulse
The tendency of an object to stay in motion or at rest until a force acts upon it is
inertia
Force
is in newton's 1kg weighs about 1 kg on 2.2 lbs
When an object is in free fall
it accelerates
Free body diagram
it shows all the forces acting on an object
The basic SI unit of mass is
kilogram
Fundamental forces of nature
magnetic, electric forces (static), gravity, strong nuclear force holds protons together inside an atom.
Distance
meters
Displacement
meters and direction. ( far from start)
What kind of speed vs time graph shows a car slowing down?
negative slope
What is speed?
object changing position over time
Which forces are drawn on a free-body diagram of an object?
only those forces that are exerted on the object
Acceleration
rate of change of speed/ velocity
When no horizontal force acts on a projectile, the horizontal velocity
remains constant
Inertia
resistance to change in motion of an object
States of motion
rest and moving at constant speed in a straight line
Line graphs
shows the relationship between 2 variables
Which of the following is true for the equation y= 4x-2?
slope=4, y intercept=-2
Which of the following is NOT a vector quantity.
speed
Velocity is
speed with direction
The speed at which air resistance and weight come to an equilibrium and downward acceleration ceases is called
terminal velocity
A magician suddenly jerks a tablecloth out from under the dishes on a table. This best demonstrates
that the dishes have inertia
This is the factor in an experiment that can be manipulated by he experimenter:
the independent variable
You have two objects. One object weighs 50 N on the moon. One object weighs 50 N on the earth. Which object would have the greatest mass?
the one on the moon.
When an object falls in a medium, such as air, it will reach a terminal velocity. How fast it reaches terminal velocity and the value of that terminal velocity depends on properties of the medium and
the shape of the falling object
Newton's law of motion that describes action-reaction pairs is the
third law
Velocity is a___________ quantity because it includes both and _________________ and __________________
vector magnitude direction
V= D/T is the equation to calculate
velocity
Vectors
velocity, displacement, acceleration, force
A kid drives 4 miles to the mall. If the speed limit is 45 miles/hr and the kid makes the trip in .03 hours. Is the kid breaking the speed limit?
yes, he is going 133 miles/hr
If the net force of an object is 0 the acceleration will be
zero. object will have a constant velocity
What is a vector? What is the difference between a scalar and vector quantity?
Vector is a direction of an object or force. The difference between a scalar and vector quantity is scalar is a measurement of quantity such as weight or temperature. Vector quantity is a measurement that tells us a direction and speed.
Explain Newton's Third Law How does the flight of a rocket depend on "action and reaction"?
Newton's third law for example if you take a balloon, blow it up and let it go air rushes out of the balloon and the balloon flies across the room. The air goes one way and the balloon goes the opposite way. The air causes the balloon to propel forward. A rocket works the same way. The rocket expels out the back rocket fuel and the rocket extends forward. Newton's third law is Ii one object exerts a force on a second, the second object exerts on equal and opposite force on the first. Newton's third law is sometimes called the law of action and reaction. The air being force out the balloon is the action and the balloon being forced forward is the reaction. The person operating the rocket who lets out the fuel that is the action and the reaction is the rocket being propelled forward.
Give four examples that demonstrate the law of "action and reaction".
Some examples that demonstrate the law of "action and reaction" is tennis ball hitting a tennis racket, skater pushing against a railing, airplane and sprinter coming out of the starting block.
What happens to the amount of air resistance on your car as you drive faster? When will an object falling through air reach terminal velocity? What is the net force and acceleration of an object that has reached terminal velocity? Compare the terminal velocity when using a standard parachute to a military parachute. Why the difference? When an object reaches terminal velocity the net force is zero. Why doesn't the object just stop?
The amount of air resistance on you car as you drive faster will increase. For example, sticking hand outside the window and feeling a breeze 10mph but when you go faster you feel a force. The net force is 0 so it wont accelerates anymore. That is considered terminal velocity, which is the final speed the object falling through air will reach.
What determines how much mass an object has? Why doesn't the mass of an object depend solely on its volume? If you were in space where there is "no gravity" and I placed in your hands objects of equal volume but different mass, how would you determine which mass was greater?
The amount of matter or material of an object determines how much mass it has. The mass of an object doesn't depend solely on its volume because the material of an object is made from determines its mass. For example, an object that is made up of a denser Material will have more mass than an object of a lighter material like such as the example in the video. A Styrofoam block can be larger than a lead block but the material the Styrofoam is composed of is lighter material than the lead block giving the lead block more mass. If I was in a space where there is no gravity and I placed my hands objects of equal volume but different mas, I would determine which mass is greater by first determining which object was made of a denser material. I would have to know how much force is needed to initiate motion in the object. The mass of an object remains the same in zero gravity and it's inertia as well. The object with more mass requires more energy to initiate movement.
What is the difference between velocity and speed? What is the difference between a +20 m/s and -20 m/s? An object moving 20 m/s east, turns and is now moving 20 m/s northeast. Did the velocity change? Justify your answer. Did the speed change? Justify your answer.
The difference between speed and velocity is speed is how fast and velocity is how fast and in what direction.
The speed at any given time is called the
instantaneous speed
Force
push or pull
Speed
rate of change of position. m/s always have time in the denomination
Which of the following objects are in free fall? (Assume that you can ignore air resistance.)
a textbook that has been thrown downward from a tall cabinet; a textbook that has been tossed upward and has left the student's hands but not yet touched any other object or surface
If you move 50 meters in 10 seconds, what is your speed?
5m/s
How much time will it take for a bug to crawl 5m across the floor at 1m/s?
5s
A car changes its speed from 0 to 25 m/s in 3.6 seconds. What is its acceleration?
6.92 m/s^2
Calculate the average velocity of the particle during the entire interval, t = 0 min to t = 1.0 min.
75 km/hr
The standard value for acceleration due to gravity at sea level is
9.8 m/s^2
Conceptual physics the old tablecloth trick Describe what happened. In terms of inertia, how would you explain what happened?
What took place in the tablecloth trick is the professor pulled a table cloth out from under a full table set without knocking any dishes on the floor In terms of inertia, The force that was exerted on the tablecloth was not exerted on the table settings because their inertia. The objects moved slightly as the cloth was moved due to the friction and their placement on top of the cloth. The dishes quickly returned to their original state due to the table under the cloth stopping their movement. It should be noted that this only works if the force exerted on the table cloth is done quickly and with excessive force to decrease the friction on the dish set.
What is meant by net force? What is the correct way to write Newton's Second Law as an equation? A force of 10 N and 50 N are applied in opposite direction to a 2 kg mass. Make a free body diagram to represent the object and forces on the object. Calculate the acceleration of the 2 kg mass.
When an object has a net force, it is either speeding up or slowing down. The net force is the sum of all forces that act on the object. Since forces are vector quantities, their sum, or net force, is a vector sum. In case of an object falling in the air, the acting forces are the gravity force (weight) W and the air resistance R .The net force is N = W + R (N, W, R are vectors) Since W and R are of opposite directions, the magnitude of their vector sum is the difference of the magnitude of W and R |N| = |W| - |R| The correct way to write Newton's second law as an equation is Fnet =ma. F is for force, M is for mass and A is for acceleration
An object is first dropped from a height of 1 meter onto a table and then is dropped from a height of one meter onto a cushion. Compare the change in momentum that an object undergoes when stopped by the cushion versus the table. When you jump off a table onto the floor you allow your knees to bend. Why? Why it is hard to bang a nail into a piece of wood if the wood is on a cushion?
When the object is dropped on the cushion the change in momentum is spread over a longer period of time, which reduces the amount of force, the object initially receives verse being dropped directly on the table, which creates a shorter period of time and a greater initial force on the object. When you jump off a table onto the floor you allow your knees to bend because this allows you to decrease your momentum over a greater period of time, which reduces the shock or force felt on your body. It is hard to bang a nail into a piece of wood if the wood is on a cushion because the force is reduced because the cushion causes the impact to be spread over a greater period of time. The less force the nail receives from the hammer the harder and longer it takes to drive the nail into the wood.
What is the definition of acceleration?
The change in velocity over time
If a wagon is accelerating at a rate of 2m/s2 2m s 2 , what is the mass of the wagon if the force acting on it is 20N?
10kg
How much force is needed to accelerate a 3000-kg car at a rate of 4m/s^2?
12000N
How many meters per second is 50 km per hour? As an object accelerates for 10s up to a final constant speed of 66 m/s, what is happening to the distance it moves each second on reaching 66 m/s? What is the difference between speed and acceleration? What is an m/s^2 a unit of?
13.8889 meters per second is in 50 km per hour. For every second that passes the object is increasing the number of meters it is passing until it reaches the top speed of 66 m/s. At this point the object is passing exactly 66 m/s as a constant assuming there is no change in speed. Speed is expressed in the amount of distance moved in a given time. Acceleration is the change of velocity in a given time. A m/s^2 is a unit of acceleration.
Calculate the velocity of the particle during the interval, t = 0.60 min to t = 1.0 min.
150 km/hr
If Tina starts out at 10 m/s, and in 10 s speeds up to 20 m/s, what is her acceleration
1m/s^2
A truck on a freeway is going 50 m/s. If it has a momentum of 100 kg*m/s, what is the mass of the truck?
2 kg
Calculate the velocity of the particle during the interval from t = 0.40 min to t = 0.60 min.
225 km/hr
Calculate the velocity of the particle during the interval from t = 0 to t = 0.20 min. (0.20min=12s)
300 km/hr
As Stephanie approaches a traffic jam, she applies a braking force of 11,000 N. Her car has a mass of 2,000 kg and is moving with a velocity of +18 m/s. What is the impulse imparted to bring the car to a stop?
36000N
Which of these is a velocity?
40 km/hr, West
If a body goes from 10m/s to 50m/s in 8 seconds, what is its acceleration?
5 m/s^2
As Milo approaches a red light, he applies a braking force of 12,000 N. His Hummer has a mass of 3,000 kg and is moving with a velocity of +22 m/s. How long will it take for Milo's Hummer to stop
5.5s
What information can be obtained by the use of crash dummies? How can there be three collisions in one crash? Distinguish between stress and strain. What happens to the human body because of the stress and strain produced in a car crash? How can the forces on occupants in crashes be reduced?
Crash test dummies can indicate where and how much force is received from impacts during crashes and other trauma. This can help us understand when and how the limits of what the human body are reached during an accident and how to reduce the force the body experiences. There are three collisions in one crash because there is the collision of the car impacting with the object, after this impact the momentum of the occupants continues until the collide with the objects in front of the (seat, steering wheel, dashboard, etc.) and behind them (usually the seat and head rest) The third collision is when the internal organs of the body impact with either the skeletal structure designed to protect it or the rigid objects outside the body such as the steering wheel or dashboard. Stress is the pressure an object feels when applied per force per an area. Strain is the change in the form of the object as a direct result of the stress set upon the object. Both are directly proportionate. When the human body undergoes stress and strain produce by a car crash, depending on the force of the crash there are varying results of a crash. All result in some form of trauma to the body, which increase proportionately with the speed and the force from the impact and the area in which the body is struck. The force can be reduced by using airbags and side impact airbags which cushion the body from harder objects within the vehicle, seat belts which can reduce the forward momentum of the body when the vehicle impacts and stops. Lastly if the vehicle is equipped with a larger crumple zone then the momentum is decreased over a longer period of time with reduces the force felt from the impact
A book sits on a desk. Which is the best free-body diagram for the book?
F norm = F grav = B
Given a force diagram like the one below, if the object is not moving, what do you know about the forces at A and B?
Fnorm = - (Fg) making the Fnet= 0 when an object is not moving.
What is Sir Isaac Newton's Third Law of Motion?
For every action there is an equal and opposite reaction.
Using the examples from the video, explain the statement, "the force is proportional to change in speed". Using the examples from the video explain why force depends on mass and the rate of change of speed. What is another name for rate of change of speed?
Force varies with mass and change of speed. For example, if you want to reduce the force you put in pedaling your bike from 0- 25K/mph than to try to zoom in 50 k/mph. It takes time to reach the speed you want to go at. It would probably take about 8 seconds to reach the speed. The more quickly you change your speed, the more force you will have. Another name for rate of change of speed is called acceleration. Force= Mass x Acceleration. A baseball player pitcher pitches the ball 50k/mph but really 10 because it is just winding up. It increases as time goes on to finally reach its top speed. You don't pitch a ball at 50k/mph it accelerates to 50. The more you accelerate, the more force you need.
How can inertia be overcome? A 5kg mass and a 1kg mass are brought to a speed of 1 m/s in 1second. Which mass required the most force? How many times more force?
Inertia can be overcome by force. A 5kg mass would require more force than a 1kg mass because it has more mass and inertia
Why did the dummy fall off the truck? Explain why F=MA is the same as FT=M X change in velocity. What is momentum? What is impulse? How is the momentum of an object changed? One egg broke the other did not. Why? Compare the change in momentum of the two eggs. Compare the impulse received by the two eggs. Two 1200 kg vehicles moving at 10 m/s come to a stop. One vehicle comes to a stop in 1 sec, the other in two seconds. Compare the change of momentum of the two vehicles. Compare the forces on the occupants of the vehicles.
The dummy fell off the truck because of Inertia. The object was at rest and wanted to remain at rest. F=MA is the same as FT=MX because they both incorporate the force equals the mass times the acceleration. Using the second equation better clarifies that the force over time equals mass times the change in velocity. Momentum is the product of an objects mass and its velocity. Impulse is the force times time. It is the amount of force acting on an object over time to change its momentum. The momentum of an object is changed by changing one of the variables in the equation such as the force over time or the velocity of the object.²he mass of an object will generally remain the same. One egg broke and the other did not because both eggs had equal mass and momentum, which would require the same impulse to reduce their momentum to zero. The wall stops the momentum for a brief period of time causing more force on the egg, which breaks its shell. The curtain spreads the force over a period of time allowing the force to be absorbed well.
The force created when the court pushes LeBron James upwards is equal to which force?
The force LeBron James drives into the court when he jumps
If a net force diagram is drawn, such as shown below, wherein the ,Fnorm at A = -(Fg) at C what do you know about the object?
The object is accelerating in the direction of the F app at B because the opposing Ffric must be negligible and Fapp at B. 0N
Describe, in detail, the motion of the particle during the interval from t = 0 to t = 0.20 min.
The particle moves at a constant velocity, from time equals 0 minutes to time equals 0.20 minutes, in a positive direction, from a position of 0km to a position of 1.0km away from the original starting position.
Describe, in detail, the motion of the particle during the interval from t = 0.40 min to t = 0.60 min.
The particle moves at a constant velocity, from time equals 0.40 minutes to time equals 0.60 minutes, in a negative direction, from a position of 0.25km to a position of 1.25km from the original starting position.
Describe, in detail, the motion of the particle during the interval from t = 0.60 min to t = 1.0 min.
The particle moves at a constant velocity, from time equals 0.60 minutes to time equals 1.0 minutes, in a positive direction, from a position of 0.25km to a position of 1.25km from the original starting position.
Describe, in detail, the motion of the particle during the interval from t = 0.20 min to t = 0.40 min.
The particle remained in an unchanged position, at 1km from the original starting position, from time equals 0.20 minutes to time equals 0.40 minutes.
What are the two parts of a vector quantity? Why is time not a vector quantity?
The two parts of a vector quantity is magnitude and direction. Time is not a vector quantity because the magnitude tells how much and direction tells us which way. Vector quantities tell us a direction and speed not time.
How do you know the particle is moving at a constant velocity, and is not accelerating, over the intervals marked A, C, and D?
This being a Position vs. Time graph, if the data on the graph makes a straight line, it has a constant slope, and therefore, a constant velocity. The change in position vs. the change in time is the same over the entire A interval, making a straight line. The change in position vs. the change in time is the same over the entire B interval, making a straight line. The change in position vs. the change in time is the same over the entire C interval, making a straight line, as well. These straight lines mean the particle is moving at a constant velocity over the intervals marked A, C, and D.
