Physics Test 2 Stroud
Which ones are true? I. Force is a scalar quantity. II. Force is a vector quantity. III. A force is a push or a pull between objects that occurs only when the objects are in physical contact. IV. Non-contact forces are also called action-at-a-distance forces.
II and IV only
A small plane increases its altitude by flying with a constant velocity at an angle θ with respect to the horizontal. Which one of the following statements is true concerning the magnitude of the net force on the plane?
It is equal to zero newtons.
Three boys of equal strength try to break a rope (and fail) by tying one end to a fence post and tugging on the other end. Three additional boys (about the same strength as the others) come along and offer their assistance. Which of the following will maximize the tension in the rope?
Keep one end of the rope tied to the post and have all six boys tug on the other end.
Inertia
Natural tendency of object to resist change in motion -property of object made of matter
When using the term "uniform circular motion," what do we mean by the term "uniform?"
The motion of the object is at a constant speed.
A skateboarder wants to cross a large playground and notices that there are large shapes painted on its asphalt surface. One shape is a large circle that covers the entire playground. Inscribed in that circle is a square, with one point at the skateboarder's feet and the other at his destination. The surface is rough and, therefore, friction is present. What path does he follow in order to minimize the work done by nonconservative forces?
The square
What would happen with net force regarding a jet moving at a constant speed of 450 m.p.h. in straight and level flight.
There is no net force acting on the jet
Force
a push or pull on an object
Non-contact force
action of a distance (gravity, electromagnetic)
acceleration always points toward where in uniform circular motion?
the center
What are some examples of an inertial frame of reference?
An airplane in straight and level flight at a constant speed. A boat moving at a constant speed along a straight path. A skydiver falling straight downward at a constant (terminal) speed.
A ball hangs on the end of a string that is connected to the ceiling so that it swings like a pendulum. You pull the ball up so that it nearly touches the end of your nose. You let the ball swing down (from rest), and then swing back, toward your face. Under which conditions will the ball strike your nose?
Only if energy is somehow added to the ball.
The greater the mass, (amount of matter) the greater?
The inertia
A satellite is in a circular orbit around a planet. A second satellite is placed in a different circular orbit that is farther away from the same planet. How do the speeds of the two satellites compare?
The speed of the second satellite is less than the speed of the first satellite.
A stone is thrown from the top of a high cliff. Air resistance is negligible. As the stone falls, which of the following is true?
The stone is never in equilibrium as it falls.
3 steps to help solve newton's second law of motion
1. identify reference frame 2. identify forces 3. redraw to free body diagram
How much energy is dissipated by a 60-W light bulb in one minute?
3600 J
In Case A an object is moving straight downward with a constant speed of 9.80 m/s, while in Case B an object is moving straight downward with a constant acceleration of magnitude 9.80 m/s2. Which one of the following is true? A nonzero net external force acts on the object in both cases. A nonzero net external force acts on the object in neither case. A nonzero net external force acts on the object in Case A only. A nonzero net external force acts on the object in Case B only.
A nonzero net external force acts on the object in Case B only. Correct. The statement is true because in Case A the object is moving with constant velocity, so the net force is zero. In Case B the object is accelerating so there is a nonzero net force.
if Fnet= 0, v=0, then a=?
A=ΔV/t= 0
A box is at rest on the floor of an elevator. Because of static friction, a force is required to start the box sliding across the elevator floor. Compare the size of the pushing force required to move the box, when the elevator is (a) stationary, (b) accelerating upward, and (c) accelerating downward. Rank these forces from smallest to largest.
Accelerating downward, stationary, accelerating upward
When given Velocity, time, ax and ay, what formula do you use?? in NL2 section
Acceleration in 2-D motion x=1/2(ax)t^2 + Vox(t) and y=1/2(ay)t^2 + Voy(t)
Which of the following statements about centripetal acceleration is true? I. An object moving with a constant velocity cannot have a centripetal acceleration. II. An object moving with a constant speed may have a centripetal acceleration.
Both I and II An object experiencing a centripetal acceleration must be moving along a circular path. Therefore, the velocity vector is constantly changing direction.
A body is moved from sea level to the top of a high mountain. Which of the following statements changes concerning the following quantities? I. The body's mass. II. The body's weight. III. The gravitational force on the body.
Both II and III change.
A ball is dropped vertically from a height . When it rebounds from the floor it attains a maximum height of 2/3h. What statement is true? Only conservative forces act on the ball. Only nonconservative forces act on the ball. Both conservative and nonconservative forces act on the ball.
Both conservative and nonconservative forces act on the ball. The gravitational force is a conservative force. However, there must be others forces, such as air friction, acting on the ball.
Engine A has a greater power rating than engine B. Which one of the following statements correctly describes the abilities of these engines to do work?
Engines A and B can do the same amount of work, but engine A can do it more quickly.
Equation for centripetal force
Fc = mv^2/r
Every force interaction has a set of what?
Force pairs
In Example 10 the Kingda Ka roller coaster starts with a speed of 6.0 m/s at the top of the drop and attains a speed of 50.3 m/s when it reaches the bottom. If the roller coaster were to then start up an identical hill, what speed would it attain when it reached the top? Assume that friction and air resistance are absent
Exactly 6.0 m/s Conservation of energy says that the object will return to the speed with which it started.
Do mass and weight equal??
NO
Suppose that the coefficients of static and kinetic friction have values such that μs = 1.4 μk for a crate in contact with a cement floor. Which one of the following statements is true? The magnitude of the static frictional force is always 1.4 times the magnitude of the kinetic frictional force. The magnitude of the kinetic frictional force is always 1.4 times the magnitude of the static frictional force. The magnitude of the maximum static frictional force is 1.4 times the magnitude of the kinetic frictional force.
The magnitude of the maximum static frictional force is 1.4 times the magnitude of the kinetic frictional force. fsMAX = μsFN and fk = μkFN, so since μs = 1.4 μk and FN is the same in both cases, therefore fsMAX = 1.4 fk and the statement is true.
A brick is resting on the surface of a flat board. As one end of the board is slowly raised, what change, if any, is there in the normal force exerted on the brick?
The normal force decreases.
The net external force acting on an object is zero. Which one of the following statements is true? The object can only be stationary. The object can only be traveling with a constant velocity. The object can be either stationary or traveling with a constant velocity. The object can only be traveling with a velocity that is changing.
The object can be either stationary or traveling with a constant velocity.
Consider two identical frictionless and banked curves - one is located on the earth, and the other is on the moon. If identical cars are to travel around each curve along a circle of the same radius, how must the speeds of the two cars compare?
The speed of the car on the earth must be greater than the speed of the car on the moon.
A rotating space station creates artificial earth-like gravity. If the size of the space station is enlarged, such that its radius increases by a factor of 4, what must happen to the speed of the station floor, so that the artificial earth-like gravity is maintained?
The speed of the station floor should increase by a factor of 2.
Which one of the following statements concerning static and kinetic frictional forces is correct? When an object is stationary, both static and kinetic frictional forces are acting on it. When an object is stationary, only the kinetic frictional force acts on it. When an object is sliding, only the static frictional force acts on it. The static frictional force acts on an object when it is stationary and the kinetic frictional force acts on it when it is sliding. Static and kinetic frictional forces act in the same direction as the normal force.
The static frictional force acts on an object when it is stationary and the kinetic frictional force acts on it when it is sliding.
Which one of the following statements concerning the two "gravitational constants" G, the universal gravitational constant, and g the magnitude of the acceleration due to gravity is true? The values of g and G depend on location. The values of g and G do not depend on location. The value of g is the same everywhere in the universe, but the value of G is not. The values of g and G are equal on the surface of any planet, but in general, vary with location in the universe. The value of G is the same everywhere in the universe, but the value of g is not.
The value of G is the same everywhere in the universe, but the value of g is not.
In which one of the following situations could an object possibly be in equilibrium? Three forces act on a single object. The forces all point along the same line, but may have different directions. Two perpendicular forces act on an object. A single force acts on an object.
Three forces act on a single object. The forces all point along the same line, but may have different directions.
IF Fnet=0 and a=0 the object is in a state of?
V=0 rest or v=constant velocity, moving
Is a force a scalar or vector quantity?
Vector
Weight is a scalar or vector?
Vector
2nd law of acceleration
When a net force acts on an object of some mass, m, then the acceleration, a, of that object that results from this force is directly proportional to the force and inversely proportional to the mass of the object.
A stone is tied to a string and swung along the path of a vertical circle at constant speed. When is the string most likely to break?
When the stone is at the very bottom of the circle.
3rd Law: Action-Reaction
Whenever one body exerts a force on a second object, the 2nd body will exert an oppositely directed force of equal magnitude on the first body Fab= -Fba both have attractive force due to gravity
Does velocity have constant speed and direction?
Yes because it is a vector
You are in a car that is traveling at constant speed on a straight and level road before it suddenly starts down a hill. What can be said of your apparent weight relative to your true weight just as the car starts down the hill? The direction of the velocity vector changes as it starts down the hill and is therefore accelerating. Hint: in what general direction is the change in the velocity vector (up or down), and therefore the acceleration?
Your apparent weight is less than your true weight.
You are standing on a scale and in a fast elevator that is taking you to the top of a tall building. The elevator slows as it reaches the top. What is true of your apparent weight as the elevator decelerates? Hint: What would be your apparent weight (i.e., the weight displayed on the scale) if the elevator stopped instantaneously?
Your apparent weight is less than your true weight.
What is the formula for Newton's Second Law?
a= (sum of F)/m or Fnet=ma don't forget that Fnet= the magnitude of= Fx cos angle* Fy sin angle* Then, divide each side by the mass Then find the magnitude of a. square root(Fx^2 + Fy^2)
A box rests on the floor of an elevator. Because of static friction, a force is required to start the box sliding across the floor when the elevator is (a) stationary, (b) accelerating upward, and (c) accelerating downward. Rank the forces required in these three situations in ascending order—that is, smallest first.
c < a < b
Complete the following statement: The net force that results when two or more forces act on an object is
determined using vector addition of the individual forces acting on the object.
Dynamic Motion
examines the causes of motion (forces, torques) and their effect on motion
If there is any interaction between an object and another object, gravity, acceleration, etc. it leads to a ?
force
A circus performer hangs stationary from a rope. She then begins to climb upward by pulling herself up, hand over hand. When she starts climbing, is the tension in the rope less than, equal to, or greater than it is when she hangs stationary?
greater than When the performer is climbing up she is accelerating upward, which is the result of increased tension in the rope.
Under what condition(s) will an object be in equilibrium?
if it is either at rest or moving with a non-zero constant velocity
Three particles have identical masses. Each particle experiences only the gravitational forces from the other two particles. How should the particles be arranged so that each one experiences a net gravitational force of the same magnitude?
in the corners of an equilateral triangle
Complete the following statement: Near the surface of the earth, the weight of an object
is the gravitational force by the earth on the object.
The speedometer of your car shows that you are traveling at a constant speed of 35 m/s. Is it possible that your car is accelerating?
possible
For uniform circular motion, the velocity is
tangent to the circle
What is the meaning of the word "normal" in the term "normal force?"
that the normal force is directed perpendicular (normal) to a surface
When a body is moved from sea level to the top of a mountain, what changes?
the body's weight The mass of an object is the same everywhere in the universe but its weight depends on the local value of gravity, which will be smaller at the top of a mountain than at sea level.
What is the chance of a light car safely rounding an unbanked curve on an icy road as compared to that of a heavy car? Assume that both cars have the same speed and are equipped with identical tires. Does the maximum safe speed depend on mass?
the same
Change in motion occurs when?
there's acceleration -occurs only as a result of interaction
How does the direction of acceleration compare with the direction of the net force that produces it?
they point in the same direction
Mass is a scalar or vector?
Scalar Measured in kg
The net external force acting on an object is zero. Which of the following statements is/are true? The object can only be stationary. The object can only be traveling with a constant velocity. The object can be either stationary or traveling with constant velocity. The object can only be traveling with a velocity that is changing.
The object can be either stationary or traveling with constant velocity.
Consider two people on the surface of the earth. One is on the equator, and the other is at the North Pole. Which person experiences the larger centripetal acceleration?
The person at the equator The magnitude of the centripetal acceleration can be obtained from a(c)=v^2/r.
In Case A, an object is moving in a straight line at a constant speed of 9.8 m/s. In Case B, an object is moving in a straight line with a constant acceleration of 9.8 m/s2. Which of the following statements is true? A nonzero net external force acts on the object in both cases. A nonzero net external force acts on the object in neither case. A nonzero net external force acts on the object in Case A only. A nonzero net external force acts on the object in Case B only.
a nonzero net external force acts on the object in Case B only
Contact force
2 objects come in contact and cause a force (normal, tension)
A car is traveling in uniform circular motion on a section of flat roadway whose radius is . The road is slippery, and the car is just on the verge of sliding off the roadway. If the car's speed were now doubled, what would be the smallest radius of the curve it could drive on without slipping?
4r
A ball starts with an initial kinetic energy of 1000 J and zero gravitational energy potential. At some later time, the ball has zero kinetic energy and 1150 J of gravitational potential energy. Which of the following is true? There are no nonconservative forces acting on the ball. A nonconservative force does positive work on the ball. A nonconservative force does negative work on the ball.
A nonconservative force does positive work on the ball.
A stone is projected at a 45° above the horizontal. At the peak of its trajectory, what types of energy does it possess?
All of these: Kinetic Gravitational potential Thermal Energy due to its mass (E=mc^2)
Can you, when given the total mechanical energy, determine the TME at any other point on a line?
All the points have the same total mechanical energy
Which of the following statements can be explained by Newton's first law? (A) When your car suddenly comes to a halt, you lunge forward. (B) When your car rapidly accelerates, you are pressed backward against the seat.
Both A and B Statement A illustrates Newton's first law because your body is initially moving forward, and when the car stops it continues forward. Statement B illustrates Newton's first law because your body tends to remain in its initial state (either rest or moving forward at some speed), so when the car accelerates forward, your body remains behind, pressing you backward in your seat.
A net external force acts on a particle that is moving along a straight line. This net force is not zero. Which one of the following statements is correct?
Both the velocity and the kinetic energy of the particle are changing.
Two cars are identical except for the tread design on their tires. They both enter an unbanked horizontal curve at the same speed. Car A cannot negotiate the turn (it slides off), but Car B can. Which tread design, the one on Car A, or the one on Car B, yields the larger coefficient of static friction between the tires and the road?
CAR B
Two horizontal forces, F1 and F2 , are acting on a box, but only F1 is shown in the drawing. F2 can point either to the right or to the left. The box moves only along the x axis. There is no friction between the box and the surface. (a) What is the direction of F2 and how does its magnitude compare to the magnitude of F1 when the acceleration of the box is positive?
F2 may be positive and have any magnitude.F2 may also be negative, provided that its magnitude is less than the magnitude of F1 .
Two horizontal forces, F1 and F2 , are acting on a box, but only F1 is shown in the drawing. F2 can point either to the right or to the left. The box moves only along the x axis. There is no friction between the box and the surface. What is the direction of F2 and how does its magnitude compare to the magnitude of F1 when the acceleration of the box is zero?
F2 must be negative and have a magnitude that is equal to the magnitude of F1 .
Two horizontal forces, F1 and F2 , are acting on a box, but only F1 is shown in the drawing. F2 can point either to the right or to the left. The box moves only along the x axis. There is no friction between the box and the surface. What is the direction of F2 and how does its magnitude compare to the magnitude of F1 when the acceleration of the box is negative?
F2 must be negative and have a magnitude that is greater than the magnitude of F1.
T or F: Uniform circular motion, in which an object moves on a circular path at constant speed, is an example of motion where the acceleration is equal to zero.
False
True or False? When an astronaut is in orbit around the earth, she is weightless?
False
An object is undergoing uniform circular motion. Which of the following changes would increase the period of the motion?The period of circular motion is equal to the circumference of the circle ( ) divided by the object's speed ( ). I. Increase the radius of the circular motion. II. Decrease the radius of the circular motion. III. Increase the speed of the object. IV. Decrease the speed of the object.
I and IV
A father and his seven-year-old daughter are facing each other on ice skates. With their hands, they push off against one another. Which of the following statements is/are true? I. Each experiences an acceleration that has a different magnitude. II. Each experiences an acceleration that has the same magnitude. III. Each experiences a pushing force that has a different magnitude. IV. Each experiences a pushing force that has the same magnitude.
I and IV only because acceleration depends on mass. So it will be different magnitude for acceleration but same magnitude for force because there was equal force between the dad and daughter.
Which of the following is/are true? I. The centripetal force points in toward the center of the circular motion. II. The centripetal force is independent of the object's mass. III. The centripetal force points in the opposite direction as the centripetal acceleration. IV. The centripetal force is a new and separate force created by nature, and therefore should appear in a free-body diagram.
I only
An object is undergoing uniform circular motion. Which of the following is/are true? I. The object is moving at constant velocity. II. The object is moving at constant speed. III. The object is accelerating.
II and III An object undergoing circular motion is moving at constant speed, but its direction of motion is constantly changing.
Which ones are false? I. Mass is a vector quantity. II. Mass is a scalar quantity. III. Mass is a measure of how much matter an object contains. IV. There is no relationship between force and mass. V. Isaac Newton developed three important laws of motion that describe the relationship between force and mass.
II and IV only
Newton's first law of motion
If net force acting on an object equals 0, then acceleration also =0 m/s^2. (Fnet=0 N a=0 m/s^2) -an object at rest continues in a state of rest or a state of motion in constant velocity unless acted upon or compelled to change that motion by same net external force
Two satellites are placed in orbit, one about Mars and the other about Jupiter, such that the orbital speeds are the same. Mars has the smaller mass. What is true about the radius of the orbit of the satellite that orbits Mars?
It is less than the radius of the orbit of the satellite orbiting Jupiter. This is because the mass of Mars is less than that of Jupiter.
In which location does a 15-kg bowling ball have the smallest mass?
Mass is the same everywhere
Which of the following statements is correct concerning satellites in orbit around the same planet? 1. The period of a satellite depends on its mass. 2. Satellites located closer to the planet have longer periods. 3. The period of a satellite is independent of the planet's mass. 4. If the orbital radius of a satellite doubles, then its period increases by a factor of 4. 5. None of the above statements are correct.
None are true
A neutron star has a mass greater than that of the sun and yet its radius is not much more than a few kilometers. Therefore, the density of a neutron star is incredible. (b)How would decreasing the radius of the sun change the acceleration of falling bodies near its surface?
The acceleration of a falling body would increase as the sun's radius decreased.
A satellite orbits the Earth in uniform circular motion. What is the direction of centripetal acceleration of the satellite?
The centripetal acceleration vector points radially inward toward the Earth.
What is the centripetal force?
The centripetal force is the net force acting on an orbiting object that maintains it in uniform circular motion.
Considering that there are only three fundamental forces in nature from which all other forces can be derived, which of the three are responsible for the forces between atoms that hold solid materials together? Electroweak force, strong nuclear force, or gravitational attraction?
The electroweak force because the bonding in materials is carried out by electrons (electric charges) because Electrons are responsible for bonding between atoms.
A neutron star has a mass greater than that of the sun and yet its radius is not much more than a few kilometers. Therefore, the density of a neutron star is incredible. (a)Suppose the sun were to shrink down to the size of a neutron star without losing any mass. How would this affect the gravitational force of the sun on an object near its surface?
The gravitational force of the sun on another object near its surface would greatly increase because the sun is now much smaller.
How does the magnitude of the centripetal acceleration depend on the radius?
The larger the radius, the smaller the magnitude of the centripetal acceleration
Suppose the coefficients of static and kinetic friction have values such that for a crate in contact with a cement floor. Which of the following statements is true? The magnitude of the static friction force on the crate is always 1.4 times as large as the kinetic friction force. The magnitude of the kinetic friction force on the crate is always 1.4 times as large as the static friction force. The magnitude of the maximum static friction force on the crate is 1.4 times as large as the kinetic friction force.
The magnitude of the maximum static friction force on the crate is 1.4 times as large as the kinetic friction force. Remember that the maximum static friction force and the kinetic friction force are both directly proportional to the normal force.
You and your friends are riding a rollercoaster. You enter a vertical loop-the-loop, turn upside-down, and then come out again at the bottom of the loop. This is similar to what the motorcycle stuntman did in the video. As you pass through the very bottom of the loop, do you feel heavier or lighter than normal?
you feel heavier
A stone is thrown with a speed v0 and returns to earth, as the drawing shows. Ignore friction and air resistance, and consider the initial and final locations of the stone. Which one of the following correctly describes the change ΔPE in the gravitational potential energy and the change ΔKE in the kinetic energy of the stone as it moves from its initial to its final location?
ΔPE = 0 J and ΔKE = 0 J The stone's motion is an example of projectile motion, in which the final vertical height is the same as the initial vertical height. Because friction and air resistance are being ignored, mechanical energy is conserved. Since the initial and final vertical heights are the same, ΔPE = 0 J. Since energy is conserved, it follows that ΔKE = 0 J also.
If I have 3 forces, F1, F2, and F3, pushing on an object, and M=sum, how would I find their net force?
ΣFnet= F1 + F2 + F3... ΣFx= F1x + F2x + F3x ΣFy= F1y + F2y + F3y [F]= squ root(Fx^2 + Fy^2) Angle theta= tan^-1(Fy/Fx)
