Physics Test 2
A 230.0 kg bear grasping a vertical tree slides down at constant velocity. What is the friction force between the tree and the bear?
2,254 N
The force of friction has 2 types, static and __________
Kinetic
Explain the difference between the mass and the weight of an object.
Mass: a) Mass is how resistant the object is to acceleration b) Mass always stays the same Weight: a) Weight is the force of gravity that acts on the body b) Weight can change on any planet since it's all based on gravity.
If the forces acting upon an object are balanced, (that is they add up to zero), then the object_____________
Must not be accelerating.
The total of all the forces acting on an object is called the ______________.
Net force
Identify each of the following as either a contact force, a field force, or not a force: Mass x Acceleration
Not a force
The _________ of a line is found by dividing the rise by the run.
Slope
Velocity
Speed with direction
When the force due to gravity equals the force due to air resistance, the speed of a falling object is called its ____________.
Terminal Speed.
An object in mechanical equilibrium is an object _____________
That can be at rest or moving at a constant speed
What would be the safest way to put up a clothesline? a) It doesn't make any difference which way the line is strung b) With the line very tight c) With some slack in the line
c) With some slack in the line
The force required to maintain an object at a constant speed in free space is equal to: a) The mass of the object b) The weight of the object c) Zero d) The force required to stop it e) None of the above
c) Zero
An object with more mass also has more ____________.
inertia.
What is the Newton formula?
kg x m/s^2
External Force
It is one that is caused by some agent outside the object or system in question.
Newton
It is the metric unit of force.
Net Force
It is the sum of all forces acting on an object.
Net force
It is the vector sum of all the external forces acting on the body.
The following forces act on an object: 9 N NORTH, 52 N SOUTH, and 55 N NORTH. What is the magnitude of the net force?
12 N
What is the maximum value of the following forces? 50 N left and 50 N right.
0N
Match the words with the statements: 1) Changing direction 2) What I do when vectors are pointed in the same direction 3) The condition of equilibrium 4) The Unit of Force 5) What I do when vectors are pointing in opposite directions Options: 1) Sum of forces = zero 2) Subtract the vectors 3) Newton 4) An acceleration to the body 5) Add the vectors
1) An acceleration to the body 2) Add the vectors 3) Sum of forces = zero 4) Newton 5) Subtract the vectors
A 15-N force and a 45-N force act on an object in opposite directions. What is the net force on the object?
30 N
A 5-N force and a 30-N force act in the same direction on an object. What is the net force on the object?
35 N
If I have a mass of 50 N, what is my weight?
50 Newtons
What's the A person weighs 650 N. What is the mass of the person?
65 KS
What is the magnitude of the resultant of a 6.0-N force acting vertically upward and a 4.0-N force acting horizontally?
7.2 N
Friction
A force of resistance to relative motion between two bodies or substances in physical contact.
Mass
A measure of an object's resistance to acceleration. A measure of the quantity of matter in an object.
Vacuum
A region that contains no matter - Outer space is very nearly a vacuum - The moon has no atmosphere, so the area above the Moon's surface is also nearly a vacuum.
A quantity that has both magnitude and direction is called a scalar quantity. True or False
False
A quantity that has only magnitude is called a vector quantity. True or False
False
Mass is a vector quantity True or False
False
Objects moving at constant speed in a straight-line path are said to be in static equilibrium.
False
True or False: If an object is speeding up, it can be in equilibrium.
False
Air resistance
The force of air pushing against a moving object. - Air resistance is also called drag - Air resistance increases as speed increases - Air resistance also increases as surface area (size) increases.
Weight
The force of gravity acting on a body. Symbolized by W.
Acceleration
The rate at which speed changes
Compared to its mass on Earth, the mass of a 10-kg object on the moon is: a) The same b) More c) Less
a) The same
A sheet of paper can be withdrawn from under a container of milk without toppling it if the paper is jerked quickly. This best demonstrates that ______________
the milk carton has inertia
Force
1) It is a push or a pull that is capable of changing the velocity of a mass. 2) A push or pull acting on a body. It usually causes some distortion of the body, a change in its velocity, or both. Force is a vector.
Match the following terms with the correct definition. There is at least one extra term that will not match any of the definition: a) Mass b) Net force c) Equilibrium d) Force e) Newton Options: 1) ____________ A unit of force able to accelerate a 1-kilogram object at 1 m/sec^2 2) ____________ The condition where the net force is zero 3) ____________ When this is zero, an object maintains its motion at constant speed and direction 4) ____________ The action that can change motion 5) ____________ A property of matter that creates inertia
1) Newton 2) Equilibrium 3) Net force 4) Force 5) Mass
The force of friction on a sliding object is 10 N. The applied force needed to maintain a constant velocity is__________________.
10 N
Two forces of 10 N both act on an object. The angle between the force 90º. What is the magnitude of their resultant?
14 N
The rate at which speed changes is called ____________.
Acceleration
The ________________________ on Earth is equal to 9.8 m/s^2
Acceleration due to gravity
According to Newton's law of inertia, a railroad train in motion should continue going forever even if its engine is turned off. We never observe this because railroad trains ___________________.
Always have forces that oppose their motion.
What do we mean by "external" force?
An external force is one caused by something outside of the body under consideration.
In light of Newton's third law of motion, why can't an internal force alone produce an acceleration of a system?
An internal force can't produce an acceleration because any internal force acting in some direction on one part of a body would produce an equal but opposite force acting on another part.
Newton's second law of motion
An object is accelerated whenever a net external force acts on it. The net force equals the objects mass x acceleration.
Newton's First Law of motion
An object will remain at rest or in uniform motion with constant velocity unless acted on by a net external force.
Identify each of the following as either a contact force, a field force, or not a force: Air Drag
Contact Force
Identify each of the following as either a contact force, a field force, or not a force: Friction
Contact Force
Identify each of the following as either a contact force, a field force, or not a force: Spring Force
Contact Force
Identify each of the following as either a contact force, a field force, or not a force: Tension
Contact Force
Identify each of the following as either a contact force, a field force, or not a force: The push of a hand
Contact Force
Identify each of the following as either a contact force, a field force, or not a force: Thrust
Contact Force
If no external forces are acting on a moving object, it will _____________________.
Continue moving at the same velocity.
True or false: The name for the PULL of a wire is called Normal force.
False
Identify each of the following as either a contact force, a field force, or not a force: Weight
Field Force
Give an example of Newton's first law in everyday life.
First example: If you kick a soccer ball inside, eventually it will stop. The reason why the soccer ball will stop, is because of friction. Second example: If you're riding a motorcycle, and you hit a bus, your motorcycle will stop but you would still be moving forward. Your motorcycle stopping is due to friction. Third example: If you throw a rock in space, it will keep on going since there is no air, gravity, and friction to stop it.
Whirl a rock at the end of a string and it follows a circular path. If the string breaks, the tendency of the rock is to ______________.
Follow a straight-line path.
A ___________ is required to change motion.
Force
The motion of an object will continue in the same direction at the same speed unless the object is acted upon by a ____________.
Force
A falling object under the influence of gravity is in ____________.
Free fall
The scientist to first introduce the concept of inertia by thinking about friction was ________________.
Galileo
If your automobile runs out of fuel while you are driving, the engine stops but you do not come to an abrupt stop. The concept that most explains why, is _______________.
Inertia
Kinetic Friction
It acts when there is relative motion between two substances in contact.
Unbalanced Force
It's a net force, acting on an object, that changes its speed and/or direction of motion.
Balanced Forces
It's when forces are in balance, acceleration is zero. Velocity is constant and there is no net or unbalanced force.
The total of all forces is called the ____________.
Net force.
The ____________ is the metric unit of force.
Newton
if you read "physics family" you should know who was born last, Galileo or Newton ______________.
Newton
An object in motion wants to stay in motion, and an object at rest wants to stay at rest, is a way of stating ________________________.
Newton's First Law
"Objects want to keep doing the same thing" is a way of stating_________________
Newton's first law.
____________ relates force, mass, and acceleration in the equation F = ma.
Newton's second law.
The metric unit most often used by scientists to measure force is the ____________.
Newtons
What are forces measured in?
Newtons or N
When a rocket ship accelerating in outer space runs out of fuel, it _______________
No longer accelerates.
Identify each of the following as either a contact force, a field force, or not a force: Acceleration
Not a force
Identify each of the following as either a contact force, a field force, or not a force: Inertia
Not a force
Identify each of the following as either a contact force, a field force, or not a force: Mass
Not a force
Terminal velocity
The constant speed that an object falling through air approaches. - At terminal velocity the force of gravity pulling down is balanced by the force of air resistance pushing up.
Define the term force and give three examples of forces.
The definition of a force is something that pulls and pushes, that has the ability to alter the velocity of a mass. Examples of a force include: Gravity Force: a force which attracts objects towards itself Examples: Earth, or Moon. Friction Force: To put forth a force by a surface while an object makes its way through it or attempts to make its way through it. Examples: Throwing rocks in space, kicking balls inside. Air Resistance Force: This force is an unique force since it is a frictional force. It reacts to objects that travel through the air. Examples: Jumping out a window, or bungee jumping.
Gravity
The force of attraction between all objects in the universe. - The kind that Earth's has causes objects to fall to Earth's surface. - This is only significant when one of the objects is very large, like the Earth. There is very, very little gravitational attraction between you and your couch - but there is some!
What are accelerations produced by
They are produced by forces
Accelerate
To change speed or direction - In common speech, this word usually means to speed up. In reality, any change in speed (speeding up or slowing down) is considered acceleration.
An object in static equilibrium is in a state of no motion.
True.
The force of gravity on an object is its ____________.
Weight
After a cannonball is fired into frictionless space, the amount of force needed to keep it going equals.: a) Zero, since no force is necessary to keep it moving b) Twice the force with which it was fired c) One half the force with which it was fired. d) The same amount of force with which it was fired e) One quarter the force with which it was fired
a) Zero, since no force is necessary to keep it moving
A girl whose weight is 500 N hangs from the middle of a bar supported by two vertical strands of rope. What is the tension in each strand? a) 0 N b) 250 N c) 500 N d) 750 N e) 1000 N
b) 250 N
You are helping your aunt move a piano on wheels from one room to another. When you push the piano horizontally, it moves at constant speed. What can you say about the piano? a) It is in static equilibrium b) It is in dynamic equilibrium c) It is in equilibrium because it doesn't experience a friction force. d) It is in equilibrium because it experiences net force opposite to the friction force
b) It is in dynamic equilibrium
Compared to its weight on Earth, a 10-kg object on the moon will weigh: a) The same amount b) Less c) More
b) Less
A scalar quantity has: a) Only direction b) Only magnitude c) Both magnitude and direction d) Neither magnitude nor direction
b) Only magnitude
What is needed to describe a vector quantity? a) Only magnitude b) Only direction c) Both magnitude and direction d) Neither magnitude nor direction
c) Both magnitude and direction
The law of inertia applies to: a) Objects at rest b) Moving objects c) Both moving and nonmoving objects
c) Both moving and nonmoving objects
An object following a straight-line path at constant speed a) Has no forces acting on it b) Has a net force acting on it in the direction of motion c) Has zero acceleration d) Must be moving in a vacuum e) None of the above
c) Has zero acceleration
The weight of a person can be represented by a vector that acts a) In a direction that depends on where the person is standing b) Perpendicular to the ground underneath the person c) Parallel to the ground d) Straight down, even if the person is standing on a hill e) All of the above
d) Straight down, even if the person is standing on a hill
Equilibrium occurs when: a) All the forces acting on an object are balanced b) The sum of the +x forces on an object equals the sum of the -x forces. c) The net force on the object is zero. d) The sum of the upward forces equals the sum of the downward forces. e) All of the above
e) All of the above
A barge is being pulled along a canal by two ropes that make equal angles with the direction in which the barge points. Assuming the two pulls on the barge equal, in what direction does the barge move? a) It oscillates back and forth between the two banks b) It moves straight ahead c) It moves in the direction of the resultant force on it d) Both A and B e) Both B and C
e) Both B and C
The law of inertia states that an object: a) Will continue moving at the same velocity unless an outside force acts on it. b) Will continue moving in a straight line unless an outside force acts on it c) That is not moving will never move unless a force acts on it. d) At rest will remain at rest unless acted on by an outside force. e) Will do all of the above
e) Will do all of the above