Midterm Review
Vector A⃗ has a magnitude of 2.00 m and vector B⃗ has a magnitude of 5.00 m. If the direction of each vector is unknown, what is the largest possible value for the magnitude of A⃗ −B⃗ ?
7.00 m
If I weigh 741 N on Earth at a place where g = 9.80 m/s2 and 5320 N on the surface of another planet, what is the acceleration due to gravity on that planet?
70.4 m/s squared
When rolled down a mountainside at 7.0 m/s, the horizontal component of its velocity vector was 1.8 m/s. What was the angle of the mountain surface above the horizontal?
75°
If you are driving 72 km/h along a straight road and you look to the side for 4.0 s, how far do you travel during this inattentive period?
80 m
At the moment shown in the figure of the earth and sun (Figure 2), what is the direction of the gravitational force acting on the earth? The possible directions are displayed in this figure (Figure 3).
A
What is the magnitude of the gravitational force acting on the earth due to the sun?
3.53×10 to the twenty second N
Which of the following quantities has units of a velocity? (There could be more than one correct choice.)
-120 m/s and/or 9.8 m/s downward
A runner runs around a track consisting of two parallel lines 96 m long connected at the ends by two semicircles with a radius of 49 m. She completes one lap in 100 seconds. What is her average velocity?
0 m/s
A volume of 100 mL is equivalent to which one of the following volumes?
0.1 L
The sum of two vectors of fixed magnitudes has the greatest magnitude when the angle between these two vectors is
0°
A weight lifter can bench press 171 kg. How many milligrams is this?
1.71 × 108 mg
Which of the following quantities has units of a displacement? (There could be more than one correct choice.)
40 km southwest and/or 186,000 mi
If you are 5'10'' tall, what is your height in meters? (2.54 cm = 1.00 in.)
1.8 m
The x component of vector is A⃗ 8.7 units, and its y component is -6.5 units. The magnitude of A⃗ is closest to
11 units
A spaceship is traveling to the Moon. At what point is it beyond the pull of Earth's gravity?
It is never beyond the pull of Earth's gravity.
The sum of two vectors of fixed magnitudes has its minimum magnitude when the angle between these vectors is
180°
If a vector A⃗ has components Ax < 0, and Ay < 0, then the angle that this vector makes with the positive x-axis must be in the range.
180° to 270°
Express 50 mi/h in units of meters per second. (1 mi = 1609 m)
22 m/s
If a vector A⃗ has components Ax > 0, and Ay < 0, then the angle that this vector makes with the positive x-axis must be in the range.
270° to 360°
The graph in the figure shows the position of a particle as it travels along the x-axis.
3 s
When Jeff ran up a hill at 7.0 m/s, the horizontal component of his velocity vector was 5.1 m/s. What was the vertical component of Jeff's velocity?
4.8 m/s
Two vectors, of magnitudes 20 mm and 50 mm, are added together. Which one of the following is a possible value for the magnitude of the resultant?
40 mm
A velocity vector has components 36 m/s westward and 22 m/s northward. What are the magnitude and direction of this vector?
42 m/s at 31∘ north of west
The reaction to the force in Part A is a force of magnitude _____, exerted on the _____ by the _____. Its direction is _____ .
5 N / earth / book / upward
The reaction to the force in Part B is a force of magnitude _____, exerted on the _____ by the _____. Its direction is _____.
5 N / table / book / downward
A runner runs around a track consisting of two parallel lines 96 m long connected at the ends by two semicircles with a radius of 49 m. She completes one lap in 100 seconds. What is her average speed?
5.0 m/s
A certain CD-ROM disk can store 600 megabytes of information. If an average word requires 9.0 bytes of storage, how many words can be stored on one disk?
6.7 × 10 to the seventh words
An oak tree was planted 22 years ago. How many seconds does this correspond to? (Do not take leap days into account.)
6.9 × 10 to the eighth
What is the mass of an object that experiences a gravitational force of 685 N near Earth's surface where g = 9.80 m/s2?
69.9 kg
A motorist travels 160 km at 80 km/h and 160 km at 100 km/h. What is the average speed of the motorist for this trip?
89 km/h
What is the value of the composite constant (Gmer2e), to be multiplied by the mass of the object mo in the equation above?
9.80 m/s squared
If a vector A⃗ has components Ax < 0, and Ay > 0, then the angle that this vector makes with the positive x-axis must be in the range
90° to 180°
An object is moving with constant non-zero velocity in the +x direction. The position versus time graph of this object is
a straight line making an angle with the time axis.
Which of the following situations is impossible?
An object has constant non-zero velocity and changing acceleration.
Six vectors (A to F) have the magnitudes and directions indicated in the figure. (Figure 1) Which two vectors, when added, will have the largest (positive) x component? Which two vectors, when added, will have the largest (positive) y component? Which two vectors, when subtracted (i.e., when one vector is subtracted from the other), will have the largest magnitude?
C and D E and F A and F
The metric system is preferred over the British system in science for the following main reason.
Conversions between metric quantities are especially easy because they are all related by factors of ten.
When you weigh yourself on good old terra firma (solid ground), your weight is 535 N . In an elevator your apparent weight is 475 N . What is the direction of the elevator's acceleration?
Downward
A 20-ton truck collides with a 1500-lb car. Which of the following statements must be true?
During the collision, the force on the truck is equal to the force on the car.
Two small balls, A and B, attract each other gravitationally with a force of magnitude F. If we now double both masses and the separation of the balls, what will now be the magnitude of the attractive force on each one?
F
Two small objects, with masses m and M, are originally a distance r apart, and the magnitude of the gravitational force on each one is F. The masses are changed to 2m and 2M, and the distance is changed to 4r. What is the magnitude of the new gravitational force?
F/4
A box is placed on a table which rests on the floor. The box pushes on the table; the reaction force to the box's push on the table is the table's push on the floor.
False
If a vector pointing upward has a positive magnitude, a vector pointing downward has a negative magnitude.
False
If a vector's components are all negative, then the magnitude of the vector is negative.
False
If the acceleration of an object is zero, then that object cannot be moving.
False
If the rockets of a spaceship in outer space (far from all gravity) suddenly lose power and go off, the spaceship will gradually slow to a stop.
False
If the velocity of an object is zero at some point, then its acceleration must also be zero at that point.
False
If the velocity of an object is zero, then that object cannot be accelerating.
False
If three vectors add to zero, they must all have equal magnitudes.
False
If you swing a bucket of water fast enough in a vertical circle, at the highest point the water does not spill out. This happens because an outward force balances the pull of gravity on the water.
False
In a collision between a huge SUV and a small hybrid car, the SUV exerts a larger force on the hybrid than the hybrid exerts on the SUV.
False
In order to get an object moving, you must push harder on it than it pushes back on you.
False
In order to lift a bucket of concrete, you must pull up harder on the bucket than the bucket pulls down on you.
False
The magnitude of the resultant of two vectors cannot be less than the magnitude of either of those two vectors.
False
You pull on a crate with a rope. If the crate moves, the rope's pull on the crate must have been larger than the crate's pull on the rope, but if the crate does not move, both of these pulls must have been equal.
False
When a 45-kg person steps on a scale in an elevator, the scale reads a steady 480 N. Which of the following statements must be true?
From the given information, we cannot tell if the elevator is moving up or down. The elevator is accelerating upward at a constant rate.
A ball is thrown downward in the absence of air resistance. After it has been released, which statement(s) concerning its acceleration is correct? (There could be more than one correct choice.)
Its acceleration is constant.
Suppose that a car traveling to the east (+x direction) begins to slow down as it approaches a traffic light. Which statement concerning its acceleration must be correct?
Its acceleration is in the -x direction.
Suppose that a car traveling to the west (-x direction) begins to slow down as it approaches a traffic light. Which statement concerning its acceleration must be correct?
Its acceleration is positive.
A rock is thrown from the upper edge of a tall cliff at some angle above the horizontal. It reaches its highest point and starts falling down. Which of the following statements about the rock's motion are true just before it hits the ground? (There could be more than one correct choice.)
Its horizontal velocity component is the same as it was just as it was launched.
A ball is thrown straight up, reaches a maximum height, then falls to its initial height. Which of the following statements about the direction of the velocity and acceleration of the ball as it is going up is correct?
Its velocity points upward and its acceleration points downward.
James and John dive from an overhang into the lake below. James simply drops straight down from the edge. John takes a running start and jumps with an initial horizontal velocity of 25 m/s. Compare the time it takes each to reach the lake below if there is no air resistance.
James and John will reach the surface of the lake at the same time.
The acceleration due to gravity is lower on the Moon than on Earth. Which one of the following statements is true about the mass and weight of an astronaut on the Moon's surface, compared to Earth?
Mass is the same, weight is less.
Which of Newton's laws could we have used to predict that the forces in Parts A and B are equal and opposite?
Newton's 1st law Newton's 2nd law
Which of Newton's laws could we have used to predict that the forces in Parts B and E are equal and opposite?
Newton's 3rd law
Which of the following changes to the earth-sun system would reduce the magnitude of the force between them to one-fourth the value found in Part A?
Reduce the mass of the earth to one-fourth its normal value. Reduce the mass of the sun to one-fourth its normal value. Reduce the mass of the earth to one-half its normal value and the mass of the sun to one-half its normal value.
A 10-kg rock and 20-kg rock are dropped from the same height and experience no significant air resistance. If it takes the 20-kg rock a time T to reach the ground, what time will it take the 10-kg rock to reach the ground?
T
A rock from a volcanic eruption is launched straight up into the air with no appreciable air resistance. Which one of the following statements about this rock while it is in the air is correct?
The acceleration is downward at all points in the motion.
Suppose that an object is moving with a constant velocity. Which statement concerning its acceleration must be correct?
The acceleration is equal to zero.
Suppose that a car traveling to the west begins to slow down as it approaches a traffic light. Which of the following statements about its acceleration is correct?
The acceleration is toward the east.
When a board with a box on it is slowly tilted to a larger and larger angle, common experience shows that the box will at some point "break loose" and start to accelerate down the board. The box begins to slide once the component of its weight parallel to the board, w||, equals the maximum force of static friction. Which of the following is the most general explanation for why the box accelerates down the board after it begins to slide (rather than sliding with constant speed)?
The coefficient of kinetic friction is less than the coefficient of static friction.
In general, how does the coefficient of static friction compare to the coefficient of kinetic friction for the same two materials?
The coefficient of static friction is greater than the coefficient of kinetic friction.
Suppose that an object travels from one point in space to another. Make a comparison between the magnitude of the displacement and the distance traveled by this object.
The displacement is either less than or equal to the distance traveled.
What is the magnitude of the gravitational force acting on the sun due to the earth?
The earth exerts 3.53×1022N of force on the sun, exactly the same amount of force the sun exerts on the earth found in Part A. _______________
When a 45-kg person steps on a scale in an elevator, the scale reads a steady 410 N. Which of the following statements must be true?
The elevator is accelerating downward at a constant rate. From the given information, we cannot tell if the elevator is moving up or down.
With the sun and the earth back in their regular positions, consider a space probe with mass mp=125kg launched from the earth toward the sun. When the probe is exactly halfway between the earth and the sun along the line connecting them, what is the direction of the net gravitational force acting on the probe?(Figure 4) Ignore the effects of other massive objects in the solar system, such as the moon and other planets.
The force is toward the sun.
A large truck collides head-on with a small car. The car is severely damaged as a result of the collision. According to Newton's third law, how do the forces acting between the truck and car compare during the collision?
The force on the truck is equal to the force on the car.
Which of the following statements are true about an object in two-dimensional projectile motion with no air resistance? (There could be more than one correct choice.)
The horizontal acceleration is always zero and the vertical acceleration is always a non-zero constant downward.
For general projectile motion, which of the following best describes the horizontal component of a projectile's acceleration? Assume air resistance is negligible.
The horizontal component of a projectile's acceleration is zero.
For general projectile motion, which of the following best describes the horizontal component of a projectile's velocity? Assume air resistance is negligible.
The horizontal component of a projectile's velocity remains a nonzero constant.
A packing crate is sitting at rest on an inclined loading ramp. How does the magnitude of the force of static friction compare to the other forces acting on the crate?
The magnitude of the force of static friction is equal to the magnitude of the component of the weight of the crate parallel to the inclined ramp.
When two objects slide against one another, which of the following statements about the force of friction between them is true?
The magnitude of the frictional force is always equal to μkn.
When two objects are in contact with no relative motion, which of the following statements about the frictional force between them is true?
The magnitude of the frictional force may be either equal to or less than μsn.
A man attempts to pick up his suitcase of weight ws by pulling straight up on the handle.(Figure 1) However, he is unable to lift the suitcase from the floor. Which statement about the magnitude of the normal force n acting on the suitcase is true during the time that the man pulls upward on the suitcase?
The magnitude of the normal force is equal to the magnitude of the weight of the suitcase minus the magnitude of the force of the pull.
Now assume that the man of weight wm is tired and decides to sit on his suitcase.(Figure 2) Which statement about the magnitude of the normal force n acting on the suitcase is true during the time that the man is sitting on the suitcase?
The magnitude of the normal force is equal to the sum of the magnitude of the man's weight and the magnitude of the suitcase's weight.
The eastward component of vector A⃗ is equal to the westward component of vector B⃗ and their northward components are equal. Which one of the following statements must be correct for these two vectors?
The magnitude of vector A⃗ must be equal to the magnitude of vector B⃗ .
An object is moving with constant velocity. Which of the following best describes the force(s) acting on the object?
The net force acting on the object is zero.
An object is moving with constant non-zero velocity. Which of the following statements about it must be true?
The net force on the object is zero.
A constant net force acts on an object. Which of the following best describes the object's motion?
The object is moving with a constant acceleration.
An object is moving in the absence of a net force. Which of the following best describes the object's motion?
The object will continue to move with a constant velocity.
If you pound a feather with a hammer, which one feels a greater force?
The size of the force is always exactly the same on both of them.
A swimmer is determined to cross a river that flows due south with a strong current. Initially, the swimmer is on the west bank desiring to reach a camp directly across the river on the opposite bank. In which direction should the swimmer head?
The swimmer should swim northeast.
For general projectile motion, which of the following best describes the vertical component of a projectile's acceleration? Assume air resistance is negligible.
The vertical component of a projectile's acceleration remains a nonzero constant.
Vector A⃗ is along the +x-axis and vector B⃗ is along the +y-axis. Which one of the following statements is correct with respect to these vectors?
The y component of vector A⃗ is equal to the x component of vector B⃗ .
In an air-free chamber, a pebble is thrown horizontally, and at the same instant a second pebble is dropped from the same height. Compare the times of fall of the two pebbles.
They hit at the same time
A boulder rolls off of a very high cliff and experiences no significant air resistance. While it is falling, its trajectory is never truly vertical.
True
The magnitude of a vector can never be less than the magnitude of any of its components.
True
A 10-kg rock and a 20-kg rock are dropped at the same time and experience no significant air resistance. If the 10-kg rock falls with acceleration a, what is the acceleration of the 20-kg rock?
a
When you weigh yourself on good old terra firma (solid ground), your weight is 535 N . In an elevator your apparent weight is 475 N . What is the magnitude of the elevator's acceleration?
a = 1.10 ms2
An auto manufacturer advertises that their car can go "from zero to sixty in eight seconds." This is a description of what characteristic of the car's motion?
average acceleration
A pilot drops a package from a plane flying horizontally at a constant speed. Neglecting air resistance, when the package hits the ground the horizontal location of the plane will
be directly over the package.
A student adds two displacement vectors that have the magnitudes of 12.0 m and 5.0 m. What is the range of possible answers for the magnitude of the resultant vector?
between 7.0 m and 17.0 m
Two displacement vectors have magnitudes of 5.0 m and 7.0 m, respectively. If these two vectors are added together, the magnitude of the sum
could be as small as 2.0 m or as large as 12 m.
Suppose a ball is thrown straight up and experiences no appreciable air resistance. What is its acceleration just before it reaches its highest point?
exactly g
Which of the following graphs represent an object at rest?
graph a (straight line across the graph)
A book weighing 5 N rests on top of a table. A downward force of magnitude 5 N is exerted on the book by the force of
gravity
A 10-kg rock and a 20-kg rock are thrown upward with the same initial speed v0 and experience no significant air resistance. If the 10-kg rock reaches a maximum height h, what maximum height will the 20-kg ball reach?
h
You are trying to cross a river that flows toward the south with a strong current. You start out in your motorboat on the east bank desiring to reach the west bank directly west from your starting point. You should head your motorboat
in a general northwesterly direction.
Two objects are dropped from a bridge, an interval of 1.0 s apart. Air resistance is negligible. During the time that both objects continue to fall, their separation
increases.
If a satellite moves with constant speed in a perfectly circular orbit around the earth, what is the direction of the acceleration of the satellite?
inward toward the earth
For general projectile motion with no air resistance, the horizontal component of a projectile's acceleration
is always zero.
When a ball is thrown straight up with no air resistance, the acceleration at its highest point
is downward
An object moving in the +x direction experiences an acceleration of +2.0 m/s2. This means the object
is increasing its velocity by 2.0 m/s every second.
You are making a circular turn in your car on a horizontal road when you hit a big patch of ice, causing the force of friction between the tires and the road to become zero. While the car is on the ice, it
moves along a straight-line path in its original direction.
A player kicks a soccer ball in a high arc toward the opponent's goal. At the highest point in its trajectory
neither the ball's velocity nor its acceleration are zero.
Do the downward force in Part A and the upward force in Part B constitute a 3rd law pair?
no
A car goes around a circular curve on a horizontal road at constant speed. What is the direction of the friction force on the car due to the road?
perpendicular to the curve inward
For general projectile motion with no air resistance, the horizontal component of a projectile's velocity
remains a non-zero constant.
For general projectile motion with no air resistance, the vertical component of a projectile's acceleration
remains a non-zero constant.
You are in a train traveling on a horizontal track and notice that a piece of luggage starts to slide directly toward the front of the train. From this observation, you can conclude that this train is
slowing down.
The reason an astronaut in an earth satellite feels weightless is that
the astronaut is falling.
A ball is thrown horizontally from the top of a tower at the same instant that a stone is dropped vertically. Which object is traveling faster when it hits the level ground below if neither of them experiences any air resistance?
the ball
When a car goes around a circular curve on a horizontal road at constant speed, what force causes it to follow the circular path?
the friction force from the road
To understand Newton's 1st law. Newton's Principia states this first law of motion: An object subject to no net force maintains its state of motion, either at rest or at constant speed in a right line. This law may be restated as follows: If the sum of all forces acting on an object is zero, then the acceleration of that object is zero. Mathematically this is just a special case of the 2nd law of motion, F⃗ =ma⃗ , when F⃗ =0. When studying Newtonian mechanics, it is best to remember the 1st law in two ways: If the net force (i.e., sum of all forces) acting on an object is zero, the object will keep moving with constant velocity (which may be zero). If an object is moving with constant velocity, that is, with zero acceleration, then the net force acting on that object must be zero. If a car is moving to the left with constant velocity, one can conclude that An object cannot remain at rest unless An object will have constant acceleration if
the net force applied to the car is zero. the net force acting on it is zero. the net force acting on it is constant in magnitude and direction.
When adding several quantities
the quantities must all have exactly the same units.
James and John dive from an overhang into the lake below. James simply drops straight down from the edge. John takes a running start and jumps with an initial horizontal velocity of 25 m/s. If there is no air resistance, when they reach the lake below
the splashdown speed of John is larger than that of James.
Consider a car that travels between points A and B. The car's average speed can be greater than the magnitude of its average velocity, but the magnitude of its average velocity can never be greater than its average speed.
true
Consider a deer that runs from point A to point B. The distance the deer runs can be greater than the magnitude of its displacement, but the magnitude of the displacement can never be greater than the distance it runs.
true
Every force has one and only one 3rd law pair force.
true
When is the average velocity of an object equal to the instantaneous velocity?
when the velocity is constant
