Physics Test 1
SI unit for power
watts
***Do Check answers at back of each section!
**
Which of the following statements about centripetal acceleration is true? More than one statement or no statements may be true.
- An object moving at a constant velocity cannot have a centripetal acceleration. - An object moving at a constant speed may have a centripetal acceleration
With a projectile object, what is acceleration along y axis?
-9.8
Suppose the total mechanical energy of an object is conserved. Which one or more of the following statements is/are true?
-If the kinetic energy decreases, the gravitational potential energy increases. -If the gravitational potential energy decreases, the kinetic energy increases. -If the kinetic energy does not change, the gravitational potential energy also does not change.
For a projectile at maximum height, what is the velocity along the y axis?
0
When a projectile object reaches its maximum height, Vy =
0
When the force points in the same direction as the displacement, theta is
0
With a projectile object, what is acceleration along x axis?
0
the work of gravity on a closed path is always
0 J
All of the following cause the acceleration of an object to double. what are they?
1. the net force acting on an object remains the same, while the mass of the object is reduced by a factor of two 2. all forces acting on the object double 3. the net force acting on the object doubles
at time t = 0 seconds, an object is observed at x = 0 m; and its position along the x axis follows the expression x = -4t + t², where the units for distance and time are meters and seconds, respectively. What is the object's displacement x between t = 1.0 seconds and t = 3.0 seconds?
16 m
The gravitational force exerted by the earth (or some other large astronomical body) on an object.
weight
This force is always directed downward, toward the center of the earth.
weight
Three cars, A, B, and C, are moving along a straight section of a highway. If the velocity of A relative to B is +60 m/s and the velocity of A relative to C is +20 m/s, then what is the velocity of C relative to B?
40 m/s
A car is traveling in uniform circular motion on a section of road whose radius is r (see the drawing.) The road is slippery and the car is just on the verge of sliding. If the car's speed were doubled, then what would have to be the smallest radius in order that the car does not slide?
4r
If the entire force is perpendicular to the displacement, the angle theta is
90
If = (44.0 km, east), = (88.0 km, 30° west of north) and = (76.2 m, north), then which equation is correct?
B + C = A
If C=A+B, then the components of C are
C = A + B
If C=A+B, then the magnitude and direction of C are
C=√Cx²+Cy²
Two cars travel along a level highway. It is observed that the distance between the cars is increasing. Which one of the following statements concerning this situation is necessarily true? a. the velocity of each car is increasing b. at least one of the cars has non zero acceleration c. the leading car has the greater acceleration d. the trailing car has the smaller acceleration e. both cars could be accelerating at the same rate
E
If an object is at rest on a horizontal surface, what forces are acting on it?
weight and normal force
The acceleration of a projectile is equal to zero when the projectile reaches the top of its trajectory.
False
A rocket is at rest on the launch pad. When the rocket is launched, its kinetic energy increases. Consider all of the forces acting on the rocket during the launch, and decide whether the following statement is true or false: The amount by which the kinetic energy of the rocket increases during the launch is equal to the work done by the force generated by the rocket's engine.
False--there are 3 forces acting on the rocket: earth's gravity, air resistance, and the force of rocket's engine
determines the acceleration g due to gravity
Gravitational constant G, earth's mass, distance r
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.
N x m
Joule
SI unit for kinetic energy
Joule
For uniform circular motion, direction of the vector is ____
NOT constant
Does direction have an effect on work?
No!
T/F: Work can be positive or negative
TRUE, depending on whether a component of the force points in the same direction as the displacement or in the opposite direction
A tennis ball is hit upward into the air and moves along an arc. Neglecting air resistance, where along the arc do the minimum and maximum speeds occur?
The maximum speed occurs at the lowest point and the minimum occurs at the highest.
An object is thrown upward at an angle Ө above the ground, eventually returning to earth. Which statement is true?
The velocity and acceleration are perpendicular only at the top of the trajectory.
T/F: Friction exists even if two objects are not in motion
True
Newton's second law
When a net force acts on an object of mass m, the acceleration that results is directly proportional to the net force and has a magnitude that is inversely proportional to the mass. The direction of the acceleration is the same as the direction of the net force. This statement is usually written as
Newton's third law
Whenever one body exerts a force on a second body, the second body exerts an oppositely directed force of equal magnitude on the first body.
For which of the following situations will the path length equal the magnitude of the displacement?
a ball is rolling down an inclined plane
If velocity or direction is not changing, then you are not
accelerating
In uniform circular motion, the direction of the velocity changes constantly, so there is always ___
acceleration
the name we give to any process where the velocity changes
acceleration
The direction of centripetal acceleration vector
always points towards the center of the circle
The force that an object exerts on the platform of a scale. It may be larger or smaller than the true weight, depending on the acceleration of the object and the scale.
apparent weight
when is centripetal acceleration greater?
at higher speeds and sharp curves (smaller radii)
the rate at which the energy is changing
average power
a scalar quantity defined as the distance traveled divided by the amount of time taken to travel this distance.
average speed
a vector quantity defined as the displacement divided by the elapsed time
average velocity
A rifle, at a height H above the ground, fires a bullet parallel to the ground. At the same instant and at the same height, a second bullet is dropped from rest. In the absence of air resistance, which bullet, if either, strikes the ground first?
both bullets
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
towards the center
centripetal
centripetal force points the direction of
centripetal acceleration
a net force that acts on an object to keep it moving along a circular path
centripetal force
net force causing centripetal acceleration
centripetal force
acceleration is a vector that points in the same direction as the
change in velocity
two ways to accelerate
change speed, direction, or both
A force is ___ when it does no net work on an object moving around a closed path, starting and finishing at the same point
conservative
The concept of potential energy is associated with a type of force known as a____ force
conservative
For uniform circular motion, speed (velocity vector) is ___
constant
The total mechanical energy is _____ along the path between the initial and final points
constant
Which of the following situations is not possible? a. a body has zero velocity and non-zero acceleration b. a body travels with a northward velocity and a northward acceleration c. a body travels in a northward velocity and a southward acceleration d. a body travels with a constant velocity and a time-varying acceleration e. a body travels with a constant acceleration and a time varying velocity
d
the surface's reaction to the forces pushing the object against the surface.
normal force
If the work done by the net force is negative, the kinetic energy of the object ____
decreases
A stone is thrown horizontally from the top of a cliff and eventually hits the ground below. A second stone is dropped from rest from the same cliff, falls through the same height, and also hits the ground below. Ignore air resistance. Which of the following quantities is or are different for the two cases? (More than one quantity may be different.)
displacement and speed just before impact with ground
If an object is at equilibrium on an inclined plane, the magnitude of the normal force will be ____ the magnitude of a component of the object's weight, as is shown in the figure.
equal to
The state an object is in if it has zero acceleration
equilibrium
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 m/s
Two buses depart from Chicago, one going to New York and one to San Francisco. Each bus travels at a speed of 30 m/s, so they have equal velocities. T/F
false-- same speed, different velocity
A push or pull
force
The push or pull required to change the state of motion of an object, as defined by Newton's second law. It is a vector quantity with units of newtons (N), dynes (dyn), or pounds (lb).
force
if the friction between the puck and the ice is negligible, and if there is no wind resistance, the acceleration of the puck is directly proportional to the ____
force
To do work, there must be
force AND displacement
Two essential elements of work
force and displacement
A force does positive work on a particle that has a displacement pointing in the +x direction. This same force does negative work on a particle that has a displacement pointing in the +y direction. In which quadrant of the x, y coordinate system does the force lie?
fourth
The force that an object encounters when it moves or attempts to move along a surface. It is always directed parallel to the surface in question.
friction
Conservative force examples
gravitational force
The greater the height, the greater the ____ energy
gravitational potential energy
kinetic energy can be converted into _____ and vice versa
gravitational potential energy
the difference between two potential energies that is related to the work done by the force of gravity
gravitational potential energy
the energy that an object of mass has by virtue of its position relative to the surface of the earth
gravitational potential energy
Twice the mass means ____ the acceleration, if the same net force acts on both objects
half
work done by kinetic frictional force appears as
heat
An object's minimum speed occurs at which point in it's projectile trajectory?
highest point
If the work done by net force is positive, the kinetic energy of the object ____
increases
In Newton's second law, the net force is only one of two factors that determine the acceleration. The other is
inertia or mass
indicates both how fast and in what direction an object is moving at a particular instant of time.
instantaneous velocity
SI unit for work
joule
An object in motion has ____ energy
kinetic
An object possesses 2 kinds of energy:
kinetic and gravitational potential energy
According to the work-energy theorem, a moving object has
kinetic energy
When a net force performs work on an object, there is always a result, called
kinetic energy
opposes the relative sliding motion that occurs between two objects
kinetic friction
tries to reduce the speed at which the surfaces slide across each other
kinetic friction
The value of gravitational potential energy is greater when the height is ___
larger
A quantitative measure of inertia. Units are kilograms (kg), grams (g), or slugs (sl).
mass
Work equates to ___
motion
In uniform circular motion, what produces the centripetal acceleration
must be a net force
A ball has a speed of 15 m/s. Only one external force acts on the ball. After this force acts, the speed of the ball is 7 m/s. Has the force done positive, zero, or negative work on the ball?
negative
Newton's second law states that the acceleration is proportional to the _____.
net force
The work-energy theorem deals with the work done by the ____, not individual forces
net-external force
The combination of kg · m/s2 is called a
newton
A sailboat is moving at a constant velocity. Is work being done by a net external force acting on the boat?
no
If the object does not move, is work done?
no
A force is ____ if the work it does on an object moving between two points depends on the path of the motion between the points
nonconservative
Kinetic frictional force is a ____ force
nonconservative
The concept of potential energy is not defined for a ____ force
nonconservative
One component of the force that a surface exerts on an object with which it is in contact. This component is directed normal, or perpendicular, to the surface.
normal force
The magnitude of frictional force is proportional to the magnitude of the ____
normal force
Two objects A and B accelerate from rest with the same constant acceleration. Object A accelerates for twice as much time as object B, however. Which one of the following statements is true concerning these objects at the end of their respective period of acceleration?
object A will travel four times as far as object B
How many speeds can a satellite have if the satellite wants to remain in orbit with a fixed radius?
only one
The force component ____ to the displacement does no work
perpendicular
A suitcase is hanging straight down from your hand as you ride an escalator. Your hand exerts a force on the suitcase, and this force does work. This work is
positive when you ride up, negative when you ride down-- the force is up, so when the displacement is up, the work is positive and when the displacement is down, the work is negative
incorporates both the concepts of work and time
power
work done per unit of time
power
the total mechanical energy is conserved when the work done by external nonconservative forces is zero
principle of conservation of mechanical energy
An object moving in two dimensions which experiences only the acceleration due to gravity
projectile motion
tension can only ___ on an object
pull
More work is done when the ____ is greater or when the ____ is greater
pushing force, displacement
the value of the velocity must be measured 'relative' to a particular observer.
relative velocity
if no net force acts on an object, then the velocity of the object
remains unchanged
Gravitational potential energy is a ___ quantity
scalar
Work is a ____ quantity
scalar
power is a ____ quantity
scalar
A quantity which can be described by a single number.
scalar quantity
Why is there no work done if the force is perpendicular to displacement?
since there is no displacement in perpendicular direction, there is no work done by perpendicular component of force
Which one of the following is not a vector quantity? a. acceleration b. average speed c. displacement d. average velocity e. instantaneous velocity
speed
velocity is a ___ and ____
speed, direction
Friction that exists even if two objects are not in motion
static friction
a force between two surfaces that prevents those surfaces from sliding or slipping across each other
static friction
opposes the impending relative motion between two objects
static friction
Nonconservative force examples
static/kinetic friction, tension, air resistance, normal force
If the work is zero, the kinetic energy ____
stays the same
The tendency of a rope (or similar object) to be pulled apart due to the forces that are applied at either end.
tension
if an object exerts a force on a rope, string, chain, or cable, we call the force
tension
kinematic formulas are only accurate if
the acceleration is constant during the time interval considered
A car travels in a straight line covering a total distance of 90 miles in 60 minutes. Which of the following statements concerning this situation is necessarily true? a. velocity of the car is constant b. acceleration of the car is non-zero c. the first 45 miles must have been covered in 30 minutes d. the speed of the car must be 90 miles per hour throughout the entire trip e. the average velocity of the car is 90 miles per hour in the direction of motion
the average velocity of the car is 90 miles per hour in the direction of motion
Joule/second
watt
In which of the following cases is the displacement of the object directly proportional to the elapsed time? a. a ball rolls with a constant velocity b. a ball at rest is given a constant acceleration c. a ball rolling with initial velocity is given a constant acceleration d. a bead falling through oil experiences a decreasing acceleration e. a rocket fired from the earth's surface experiences an inreasing acceleration
the ball rolls with a constant velocity
An object moving along a straight line is decelerating. Which one of the following statements concerning the object's acceleration is necessarily true?
the direction of the acceleration is in the direction opposite to that of velocity
The net external force acting on an object is zero. Which one of the following statements is true?
the object can either be stationary or traveling at constant velocity
Consider two people, one on the earth's surface at the equator and the other at the north pole. Which has the larger centripetal acceleration?
the person at the equator
During the final stages of descent, a sky diver with an open parachute approaches the ground with a constant velocity. There is no wind to blow him from side to side. Which one of the following statements is true?
the sky diver is in equilibrium because two forces acting on him, the force of gravity and the upward force of the parachute
Starting from rest, a particle confined to move along a straight line is accelerated at a rate of 5 m/s². Which one of the following statements accurately describes the motion of this particle?
the speed of the particle increases by 5 m/s during each second
When a car moves at a steady speed around an unbanked curve, the centripetal force keeping the car on the curve comes from
the static friction between the road and the tires
The sum of KE and PE
total mechanical energy
direction of the centripetal acceleration
toward the center of the circle
T/F: All types of energy can be converted from one form to another
true
equation for y max
use regular y equation
Centripetal acceleration is a ____ quantity
vector
Two perpendicular vectors which added together produce the original vector.
vector components
A quantity which can be adequately described by a number (magnitude) and a direction.
vector quantity
An object with kinetic energy can perform ____ if it is allowed to push or pull on another object
work
Why does a moving object have kinetic energy?
work is done to accelerate the object from rest to a speed
the relationship between work to the change in kinetic energy
work-energy theorem
When a projectile object reaches its maximum height, y =
y max
Can an object accelerate if it's moving with a constant speed?
yes!
Even if force is applied, work is ____ if distance is zero
zero
constant velocity means ___ horizontal acceleration
zero
if an object is at equilibrium then it has ___ acceleration
zero