Physics exam 1

Fill in the blanks: The Standard International unit for mass is the _______. The Standard International unit for force is the _______.

1.) kg 2.) newton

The acceleration due to gravity is 10m/s/s. A rock is thrown vertically into the air. At the top of its path, its acceleration in meters per second per second is about 0. between 0 and 10. greater than 10. 10. none of these

10

on earth's surface, all objects accelerate downward at _______

10 m/s2 all objects fall at the same rate

True or false? A body acted on by no net force moves with constant velocity(which may be zero)

true

When an object is thrown upward, how much speed does it lose each sec

10 m/s

What is the gain in speed per second for a freely falling object?

10 m/s/s

How does the direction of acceleration compare with the direction of the net force that produces it?

The acceleration is in the direction of the net force. Acceleration is proportional to net force and inversely proportional to mass.

If the net force acting on a sliding block is somehow tripled, by how much does the acceleration increase?

The acceleration is tripled

Is acceleration directly proportional to mass, or is it inversely proportional to mass? Give an example.

The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object

State Newton's second law of motion.

The acceleration of an object is directly proportional to the net force acting on the object, is in the direction of the net force and is inversely proportional to the mass of the object. vector sum of forces = mass * acceleration

What will be the kinetic energy of a pile driver ram when it undergoes a 10 kJ decrease in potential energy?

The kinetic energy will increase The sum of an object's potential and kinetic energies is called the object's mechanical energy. As an object falls its potential energy decreases, while its kinetic energy increases. The decrease in potential energy is exactly equal to the increase in kinetic energy

Cite Newton's first law of motion

The law of inertia: Every object continues in a state of rest or of uniform speed in a straight line unless acted on by a nonzero net force. (If an object is undertake influence of only one force, it cannot be in equilibrium. net force couldn't be zero)

Consider a book that weights 15N at rest on a flat table. How many newtons of support force does the table provide? What is the net force on the book in this case?

The support force is 15N. The net force is 0

Someone standing at the edge of a cliff throws one ball straight up and another ball straight down at the same initial speed. Neglecting air resistance, the ball to hit the ground below the cliff with the greatest speed will be the one initially thrown downward. upward. They will both hit with the same speed.

They will both hit with the same speed.

True or false? It is possible for an object to have motion in the absence of forces on the object. It is possible to have forces on an object in the absence of motion of the object.

True

Characteristics of forces

Unit: N, the newton; 1 N = 1 kg m/s2 Acceleration of a mass is proportional to the exerted force Forces are vectors

Cite three examples of a vector quantity and three examples of a scalar quantity.

Vector quantity: force, acceleration, momentum Scalar quantity: mass, volume, speed, mass

A Mack truck and a Volkswagen traveling at the same speed have a head-on collision. The vehicle to undergo the greatest change in velocity will be the Volkswagen. Mack truck. both the same

Volkswagon

How does impulse differ from force?

impulse differs because it is measuring the force changes over time

Net force

is the vector sum of all forces on an object

Consider these measurements: 10 m, 10 m/s, and 10 m/s2. Which is a measure of distance, which of speed, and which of acceleration

speed- m/s; distance- m; acceleration- m/s2

Which is normally greater, static friction or sliding friction on the same object?

static friction

Distinguish between speed and velocity

velocity is the speed with a direction, while speed does not have a direction. Speed is a scalar quantity—it is the magnitude of the velocity.

Can force be expressed in units of pounds and also in units of newtons?

yes

If a car moves with constant a velocity, does it also move with a constant speed? yes no sometimes, it depends on the direction

yes

units of energy

(1) Joules (J) = 1kgm2/s2

If a freely falling object were somehow equipped with a speedometer on a planet where the acceleration due to gravity is 20 m/s/s, then its speed reading would increase each second by 20 m/s. 10 m/s. 30 m/s. 40 m/s. depends on its initial speed

20 m/s

A 4-kg ball has a momentum of 12 kg∙m/s. What is the ball's speed? 3 m/s 4 m/s 12 m/s 48 m/s none of these

3 m/s

A bow is drawn so that it has 40 J of potential energy. When fired, the arrow will ideally have a kinetic energy of less than 40 J. 40 J. more than 40 J

40 J

What is the net force on a cart that is pulled to the right with 100 pounds and to the left with 30 pounds?

70 lbs

contact force

A force that is exerted only when two objects are touching.

A karate chop delivers a force of 2000 N to a board that breaks. The force that the board exerts on the hand during this event is A. 2000 N. B. less than 2000 N. C. greater than 2000 N. D. Need more information.

A. 2000 N

An Olympic high diver has gravitational potential energy because of her height. As she dives, what becomes of her energy just before she hits the water? (A)Her gravitational potential energy is converted into kinetic energy (B)Her gravitational potential energy is converted into elastic potential energy (C)Her gravitational potential energy remains constant (D)Her gravitational potential energy increases

A. GPE is converted into KE

Consider hitting a baseball with a bat. If we call the force of the bat against the ball the action force, identify the reaction force. A.The ball exerts a reaction force on the bat B.The bat exerts a reaction force on the ball C.The baseball player exerts a reaction force on the bat D.The baseball player exerts a reaction force on the ball

A. the ball exerts a reaction force on the bat

Why does Colin Kaepernick (49ers quarterback) wear a football helmet? (A)To increase the time over which a collision occurs therefore reducing the force exerted on his head. (B)To decrease the time over which a collision occurs therefore reducing the force exerted on his head. (C)To decrease the impulse of a collision therefore reducing the force exerted on his head. (D)To decrease the change in momentum during a collision therefore reducing the force exerted on his head.

A. to increase the time over which a collision occurs therefore reducing the force exerted on his head

If Earth shrank with no change in its mass, what would happen to your weight at the surface? (A)Your weight would increase (B)Your weight would decrease (C)You weight remains the same

A. your weight would increase. decrease radius, force increases

What is the effect of air resistance on the acceleration of falling objects? What is the acceleration with no air resistance?

Air resistance slows objects down, therefore decreasing acceleration. When there is no air resistance, acceleration is the same for two falling objects regardless of their weights.

When a star collapses to form a black hole (A)its radius increases and the gravitational force increases at its surface (B)its radius decreases and the gravitational force increases at its surface. (C)its mass increases and the gravitational force increases at its surface. (D)its mass decreases and the gravitational force decreases at its surface.

B

If a car driving down the road doubles its speed what happens to its kinetic energy? KE = 1/2mv2 (A)Kinetic energy doubles (B)Kinetic energy quadruples (C)Kinetic energy stays the same (D)Kinetic energy halves

B. kinetic energy quadruples

Acceleration

By changing speed, direction or both speed and direction, how quickly and in what direction velocity changes is acceleration

If the Sun collapsed to become a black hole, the Earth's gravitational attraction to it would (A)increase .(B)decrease. (C)stay the same.

C stay the same The distance (d) will stay the same. The gravitational force around the sun is greater. but forces for those that are far away would not change

To transfer the greatest momentum to an object (A)exert the largest force possible (B)extend that force for as long a time as possible (C)both of the above (D)none of the above

C. both

You are driving your car down the highway at constant velocity. Which of the following are true? (A)The car's momentum is constant but not its kinetic energy. (B)The car's kinetic energy is constant but not its momentum. (C)Both the car's kinetic energy and momentum are constant.(D)Neither the car's kinetic energy nor momentum are constant.

C. both kinetic energy and momentum are constant (because mass can't change) if speed is not changing, momentum is not changing

constant velocity

Constant speed and constant direction. motion in a straight line at a constant speed

Decreasing momentum

Extend the time of impact

action-reaction

For every action there is an equal and opposite reaction

State Newton's third law of motion.

For every force (action) there is an equal and opposite force (reaction).

G vs g

G is the universal gravitational constant; it is the same everywhere g is the acceleration gravity; it will vary by location

What relationship did Galileo discover about a ball's acceleration and the steepness of an incline? What acceleration occurs when the plane is vertical?

Galileo discovered that a ball rolling down an in incline plane picks up the same amount of speed in successive seconds, that is the ball rolls with unchanging acceleration - constant acceleration. The gain per second is its acceleration. As the steepness of the incline increases, the acceleration also increases

The planet Jupiter is about 300 times as massive as the Earth, yet on its surface you would weigh only about 3 times as much. This is because a. Jupiter is significantly farther from the Sun. b. your mass is 100 times less on Jupiter. c. Jupiter's radius is 10 times the Earth's radius. d. you are 100 times more weightless there. e. none of these

Jupiter's radius is 10x the earth's radius

What happens to your weight while standing on a scale in an elevator accelerating downward

Less compression in scale strings; apparent weight is less

Where do you weigh more - at the bottom of Death Valley or atop one of the peaks of the Sierra Nevada? Why?

On the mountain peak, you would be farther from Earth's center than at sea level, so the gravitational attraction would be slightly less. Therefor, you would weigh less.

Distinguish between velocity and acceleration

Speed is the distance covered in a unit of time while acceleration is the rate of change of speed. The unit of speed in the metric system is meters per second (m/s) while that of acceleration is meters per second squared (m/s2). Speed is a scalar quantity while acceleration is a vector quantity.

Is acceleration proportional to net force, or does acceleration equal net force?

The magnitude of the acceleration is directly proportional to the net force applied, and inversely proportional to the mass of the object.

inverse square law

The magnitude of the force varies as the inverse square of the separation of the particles

constant acceleration

The rate at which the velocity changes each second is the same. The speed changes by 10 m/s every second

black hole

The remains of a star that has collapsed under its own gravitational force. a region of space having a gravitational field so intense that no matter or radiation can escape.

Escape speed

The speed that a projectile, space probe, or similar object must reach to escape the gravitational influence of Earth or of another celestial body to which it is attracted.

Inertia

The tendency of an object to resist a change in motion

What relationship does mass have with inertia?

The tendency of an object to resist changes in its state of motion varies with mass. Mass is that quantity that is solely dependent upon the inertia of an object. The more inertia that an object has, the more mass that it has. A more massive object has a greater tendency to resist changes in its state of motion.

True or false? If the net force on a body is 0, the velocity will not change

True

What happens to an object's velocity and acceleration when in the same direction? opposite direction?

When an objects velocity and acceleration are in the same direction, the object is speeding up; when an object's velocity and acceleration are in the opposite direction, the object is slowing down

proportional, inversely proportional

When two things are directly proportional to each other, as one increases, the other also increases. When two things are inversely proportional to each other, as one increases, the other decreases.

Earth pulls down on you with a gravitational force that you call your weight. Do you pull up on the Earth with the same amount for force?

Yes, it is known as support force

When a star collapses to form a black hole a. the escape velocity exceeds the speed of light. b. its mass increases and the gravitational force increases at its surface. c. its size increases and the gravitational force increases at its surface. d. the planets that are circling the sun will get sucked in and destroyed.

a.

Two objects move toward each other because of gravity. As the objects get closer and closer, the acceleration of each a.) increases b.) decreases c.) remains constant

a

field force

a force that is exerted without contact. act through empty space

What is sliding friction?

a force that opposes the direction of motion of an object as it slides over a surface (stop objects already sliding)

Force

a push or pull on an object

A scalar is

a quantity that does not have a direction Examples: time, temperature, energy, mass Scalars are manipulated with ordinary algebra

Equilibrium

a state in which opposing forces or influences are balanced (no change). An object that is under only one force cannot be in equilibrium. The net force could not be zero.

A black hole has a. about the same mass as the original star from which it formed. infinite mass. b. a mass that widely fluctuates. c. about half the mass of the star from which it forme

a.

If you are backing up or speeding up, your acceleration is directed a. backwards b. forwards c. nowhere d. to the left

a. backwards

A 300-kg bear grasping a vertical tree slides down at constant velocity. The friction force between the tree and the bear is (hint: you are given the mass of the bear, not the weight) a.) 3000 N. b.) 300 N. c.) 30 N. d.) more than 3000 N

a.) 3000 N

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 a.) Follow a straight path or b.) continue to follow a circular path

a.) Follow a straight path

If the mass of the Earth somehow increased with no change in radius, your weight would a.) increase b.) decrease c.) stay the same

a.) increase

Two objects move toward each other because of gravity. As the objects get closer and closer, the force between them a.) increases b.) decreases c.) remain constant

a.) increases

A bowling ball at rest on a table is in equilibrium. Is the ball in equilibrium when it moves at constant speed in a straight line path across the table? a.) yes b.) no c.) sometimes, it depends on the speed

a.) yes

Equation of acceleration

acceleration= change of velocity/time interval

A feather and a coin dropped in a vacuum fall with equal accelerations. momenta. kinetic energies. forces. none of these

accelerations

A moving object has momentum. energy. velocity. speed. all of these

all of these

What relationship does mass have with weight?

an object's weight is directly proportional to its mass. weight=mg if you triple the object's mass, the weight is tripled

A heavy object and a light object are dropped at the same time from rest in a vacuum. The heavier object reaches the ground sooner than the lighter object. later than the lighter object. at the same time as the lighter object.

at the same time as the lighter object.

An object is shot vertically upward, while it is rising: a. its velocity and acceleration are both upward b. its velocity is upward and its acceleration is downward c. its velocity and acceleration are both downward d. its velocity is downward and its acceleration is upward

b

When the distance between two stars decreases by half, the force between them a. decreases by one-half. b. increases to four times as much. c. stays the same. d. increases to twice as much. e. decreases by one-quarter.

b.

Which of the following describes the relationship between mass and acceleration according to Newton's second law? A.Acceleration is proportional to mass B.Acceleration is inversely proportional to mass C.An object with mass cannot accelerate D.Acceleration and mass are not related

b. acceleration is inversely proportional to mass

When a star collapses to form a black hole, a. its radius increases and the gravitational force increases at its surface b. its radius decreases and the gravitational force increases at its surface c. its mass increases and the gravitational force increases at its surface d. its mass decreases and the gravitational force decreases at its surface

b. its radius decreases and the gravitational force increases a its surface

The event horizon of a black hole is a. the point in time when a black hole comes into being. b. the surface below which no matter or energy can escape. c. the physical surface of the black hole. d. the surface where light becomes trapped in a circular orbit around the black hole.

b. the surface below which no matter or energy can escape

A hockey puck is set in motion across a frozen pond. If ice friction and air resistance are neglected, the force required to keep the puck sliding at constant velocity is a.) the mass of the puck multiplied by 10 m/s/s. b.) 0N c.) the weight of the puck divided by the mass of the puck. d.) equal to the weight of the puck. e.) none of the above

b.) 0 N

To impart the greatest momentum to an object, should you exert the largest force possible, extend that force for as long a time as possible, or both? Explain.

both

A Mack truck and a Volkswagen traveling at the same speed collide head-on. The impact force is greatest on the a.) Mack truck. b.)Volkswagen. c.)is the same for both

c.) Is the same for both

A package falls off a truck that is moving at 30 m/s. Neglecting air resistance, the horizontal speed of the package just before it hits the ground is a.) less than 30 m/s b.) less than 30 m/s but larger than zero c.) about 30 m/s

c.) about 30 m/s

A hockey puck is set in motion across a frozen pond. If ice friction and air resistance are neglected, the horizontal force required to keep the puck sliding at constant velocity is a.) equal to the product of its mass times its weight. b.)equal to its weight divided by its mass. c.) zero. d.) equal to its weight.

c.) zero

A 10-kg brick and a 1-kg book are dropped in a vacuum. The force of gravity on the 10-kg brick is a.) the same as the force on the 1-kg book. b.) zero. c.)10 times as much as the force on the 1-kg book.

c.)10 times as much as the force on the 1-kg book.

If an object falls with constant acceleration, the velocity of the object must continually decrease. be constant also. continually change by the same amount each second. continually change by varying amounts, depending on its speed. none of these

continually change by the same amount each second.

Which of the following statements is correct? a. it is possible for an object to have motion in the absence of forces on the object b. it is possible to have forces on an object in the absence of motion of the object c. neither d.both

d. both (asteroid is in motion but no forces on it. an object at rest will still have forces on it)

A baseball player hits a ball with a bat. The action force is the impact of the bat against the ball. The reaction to this force is the a.) grip of the player's hand against the ball. b.) air resistance on the ball. c.) weight of the ball. d.) force of the ball against the bat. e.) none of these

d.) Force of the ball against the bat

An example of a force is a.) a push or a pull. b.) friction. c.) weight. d.) All of the above.

d.) all of the above

A ball tossed vertically upward rises, reaches its highest point, and then falls back to its starting point (ignore air resistance). During this time the acceleration of the ball is always in the direction of motion. opposite its velocity. directed upward. directed downward.

directed downward

What two units of measurement are necessary for describing speed? velocity distance time direction

distance and time

A freight train rolls along a track with considerable momentum. If it rolls at the same speed but has twice as much mass, its momentum is unchanged. zero. quadrupled. doubled.

doubled

which of the following is a vector quantity? a. acceleration b. velocity c. momentum d. force e. all of the above

e. all

The newton is a unit of density inertia force. mass

force

If you double the force of an object what happens to the acceleration?

if force is constant, as mass is increased, acceleration decreases. resistance to changes in motion (also known as INERTIA.) ... If the net force on an object is doubled, its acceleration will double If the mass of an object is doubled, the acceleration will be halved

What relationship does mass have with inertia

mass is a measure of inertia

What happens to your weight in an elevator accelerating upward

more compression in scale strings; apparent weight is greater

What happens to your weight at constant speed in an elevator

no change in weight (normal)

If the Sun collapsed to become a black hole, the Earth's gravitational attraction to it would be less. no different. more.

no different

impulse

objects exchange momentum via impulses impulse = force * time = change in momentum

gravitational potential energy

potential energy stored in the gravitational forces between objects proportional to mass and height Gravitational PE = mgh (mass * height)

Equation of speed

speed = distance/time

terminal velocity

the constant velocity of a falling object when the force of air resistance is equal in magnitude and opposite in direction to the force of gravity

kinetic energy

the energy an object has due to its motion 1/2mass * speed2

Free fall

the motion of a falling object when the only force acting on it is gravity

elastic potential energy

the potential energy of an object that is stretched or compressed (Spring) PE = 1/2kd2 (spring constant x distance spring Is compressed)

net force

the vector sum of all the forces on an object

free fall equation

v=gt

What is weight equal to

weight is equal to the magnitude of the gravitational force exerted on the object (weight will vary with location)

If you push on a crate with a force of 100 N and it slides at constant velocity, how much is the friction acting on the crate?

100N. The fact that the net force on the crate equals zero means that the force of fricition must equal and opposite to our pushing force

A person is attracted toward the center of the Earth by a 500-N gravitational force. The force of attraction of the Earth toward the person is very, very large. very, very small. 500 N

500N

A scaffold that weighs 400 N supports two painters, one 500 N and the other 400 N. The tension in the rope on the left is 800 N. What is the magnitude of the tension in the rope on the right?

500N

An object is in free-fall. At one instant, it travels at a speed of 50 m/s. Exactly 1 s later, its speed is about 50 m/s. 55 m/s. 100 m/s. 60 m/s. 25 m/s.

60 m/s

Why is a black hole invisible?

A black hole is invisible because it's gravity is strong enough to pull in and trap light.

What does it mean to say that momentum (or any quantity) is conserved?

A conserved quantity cannot be created or destroyed; it may be transformed from one form to another, but the total amount of energy never changes

A vector is

A quantity that has both size and direction.

Vector

A quantity that has magnitude and direction

What are the two ways to increase impulse?

Apply the greatest force for as long as possible

State Newton's law of universal gravitation in words. Then do the same with one equation.

Every body in the universe attracts every other. body with a force that is directly proportional to the product of their masses and inversely proportional to the square of distance between them. G(m1*m2/d2)

Newton's First Law

Every object continues in a state of rest or of uniform speed in a straight line unless acted on by a nonzero net force. In other words, an object in motion tends to stay in motion, an object at rest tends to stay at rest.

True or false? An unbalanced force on a body will always impact the object's speed

False

true or false? An unbalanced force on an object will always change the object's direction

False

Why do we say that force is a vector quantity?

Force involves both magnitude and direction

If a freely falling object were somehow equipped with an odometer to measure the distance it travels, then the amount of distance it travels each succeeding second would be less and less. greater than the second before. constant.

Greater than the second before

How great is the force of friction compared with your push on a crate that doesn't move on a level floor?

If an object is to move at a constant velocity, a force equal to the opposing force of friction must be applied so that the two forces exactly cancel each other. No friction exists on a crate that sits at rest on a level floor. But, if you push the crate horizontally, you'll disturb the contact surfaces and friction is produced. If the crate is still at rest, then the friction that opposes motion is just enough to cancel your push.

Would the springs inside a bathroom scale be more compressed if you weighed yourself in an elevator that moved upward at constant velocity? Downward at constant velocity?

If the elevator accelerated upward, your weight would be heavier (more compressed) and if it were going downward, you would weigh less (Less compressed)

Would the springs inside a bathroom scale be more compressed or less compressed if you weighed yourself in an elevator that accelerated upward? Downward?

If the elevator accelerated upward, your weight would be heavier (more compressed) and if it were going downward, you would weigh less (Less compressed)

What does it mean to say that a moving object has inertia? Give an example

Inertia is an object's resistance to change in motion. If you rip a tablecloth off a table with heavy objects on it, the objects will want to stay in place.

A moving car has kinetic energy. If is speeds up until it is going 4 times as fast, how much kinetic energy does it have in comparison?

it will have 16x more kinetic energy if the speed of the object triples the kinetic energy becomes nine times the initial kinetic energy. It turns out that an object's kinetic energy increases as the square of its speed. A car moving 40 mph has four times as much kinetic energy as one moving 20 mph, while at 60 mph a car carries nine times as much kinetic energy as at 20 mph. Thus a modest increase in speed can cause a large increase in kinetic energy.

A kilogram is a measure of an object's

mass

If an object has kinetic energy, then it also must have impulse. force. momentum. acceleration.

momentum

Two objects, A and B, have the same size and shape, but A is twice as heavy as B. When they are dropped simultaneously from a tower, they reach the ground at the same time, but A has greater speed. momentum. acceleration. all of these none of these

momentum

Which has a greater momentum, a heavy truck at rest or a moving skateboard?

moving skateboard

Can you physically touch a person without that person touching you with the same amount of force?

no. Every action has an equal and opposite reaction

An apple hanging from a limb has potential energy because of its height. If it falls, what becomes of this energy just before it hits the ground? When it hits the ground?

potential energy becomes kinetic energy which becomes thermal energy

What is static friction?

the force that resists the initiation of sliding motion between two surfaces that are in contact and at rest/not moving (prevent objects starting to slide)

Consider hitting a baseball with a bat. If we call the force of the bat against the ball the action force, identify the reaction force.

the reaction force is the ball against the bat

support force (normal force)

the upward force that balances the weight of an object on a surface. The normal force (upward support force) equals the weight (Force of gravity pushing downward). This is equilibrium. And the net force is 0 because it is balanced