Physics Midterm
Conservation of Energy COnservation of Energy and machines
In the absence of external work input or output, the energy of a system remains the unchanged. Energy cannot be created or destroyed. energy is not lost. Input=output [Fd] input = [Fd] output
Inertia
The property of things to resist change in motion
A car traveling at 22 m/s comes to an abrupt halt in .2 s when it hits a tree. What is the deceleration in meters per second squared of the car.
110 22m/s / 0.2s = 110
if a rocket initially at rest accelerates at a rate of 25 m/s^2 for 1 min its speed will be
1500 m/s 25*60
a pot falls from a ledge and hits the ground 2 seconds later. the speed with which it hits the ground is about
20 m/s^2
According to the work-energy theorem, in the absence of friction, if you do 300 J of work on a cart, you'll increase its kinetic energy by 300 J squared. appreciably more than 300 J. 300 J. somewhat less than 300 J.
300 J law of conservation of energy
Density
A measure of mass per volume for a substance
Impulse-momentum relationship
Impulse is equal to the change in momentum of the object upon which the impulse acts Ft= change in mv
Newtons second law
LAW OF ACCELERATION -when a net force acts on an object, it will accelerate The acceleration produced by a net force on an object is directly proportional to the net force, is in the same direction as the net force and is inversely proportional to the mass of the object. - Force is proportional to acceleration [the horse pushed on the rock with more force than Newton did, so the horse is going to make the rock accelerate more. Also, Mass of the guy named Newton was less, therefore, the force was less. Mass of horse is more therefore applied force is more] - Acceleration is INVERSELY proportionate to the mass. [ force of hand accelerates brick. that same force accelerates 2 bricks 1/2 as much that same force accelerates 3 bricks 1/3 as much
Newtons third law
LAW OF ACTION-REACTION Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object
Newtons first law of motion
LAW OF INERTIA Every object continues in it's state of rest or a uniform speed in a straight line, unless acted on by a nonzero force
Which requires more power, lifting a 25-kg. bag of cement 10 m vertically in 1 minute, or lifting a 50-kg. bag 5 m vertically in 2 minutes? 25 50 both the same
Newton x meter = work convert to Newtons by multiplying by gravity [9.8] 50kg x 9.8= 490 J 490 x 5= 2450 J 25kg x 9.8= 245 J 245 x 10= 2450 J
When a 10-kg block is simultaneously pulled westward with 25 N and eastward with 15 N, it undergoes an acceleration of
None of the above. The answer should be 1 m/s2 to the west. acceleration= 10N/10kg
Kinetic Energy
The energy of motion KE= 1/2mv^2
Air resistance
The force of friction acting on an object due to its motion through air.
If a tractor slams into a haystack and comes to rest, how will the impulse that acts on it compare with slamming into a brick wall and coming to rest? The impulse will be more. The impulse will be the same either way. The impulse will be less. None of these.
The impulse will be the same either way. this is in accord with Newton's third law. Forces are equal in magnitude and they act over the same time, so impulses are equal in magnitude and opposite in direction also.
Vector Quanitity
a quantity that specifies direction as well as magnitude
velocity
a vector quantity that specifies both the speed of an object and its direction of motion
A 1-kg chunk of putty moving at 5 m/s collides and sticks to a 5-kg bowling ball initially at negative 1 m/s . The bowling ball and putty then have a momentum of a. 0 kg m/s. b. 1 kg m/s. c. - 4 kg m/s. d. 5 kg m/s. e. more than 5 kg m/s.
a. 0 kg * m/s Inital Momentum = Final Momentum 5[1] = 5[-1]
The power expended when a 100 N barbell is raised 2.0 m in 2 s is a. 100 W. b. 4 W. c. 8 W. d. dependent on the mass of the barbell.
a. 100 W. 1. power= work/time 2. work= force/distance work= 100N x 2= 200 power = 200/2 power= 100
A ball is moving at 12 m/s and has a momentum of 48 kg*m/s. What is teh ball's mass? a. 4 kg b. 12 kg c. 48 kg d. 192 kg e. none of these
a. 4 kg 48/12
If the radius of Earth somehow increased with no change in mass, your weight would a. decrease b. increase c. not change
a. decrease
Earth's gravitational field a. does not cancel inside earth b. can cancel both inside and outside earth c. is only above and beyond Earth's surface
a. does not cancel inside earth
The conservation of momentum is not related to a. newtons fourth law b. action and reaction c. newtons third law
a. newtons fourth law
A sheet of paper can be withdrawn from under a container of milk without toppling it if the paper is jerked quickly. Because of its inertia, a. the milk carton has no acceleration b. there is an action-reaction pair of forces c. gravity tends to hold the milk carton secure d. the milk carton has inertia e. none of these
a. the milk carton has no acceleration
The attraction of a persons body toward earth is called weight. The other way of describing this force is a. the pulling of a person's body towards Earth b. Earth's surface pushing against the person's body. c. the person's body pulling on Earth's surface d. none of these
a. the pulling of a person's body towards Earth
An object travels 4m in the 1st second of travel, 4m again duirng the 2nd second of travel, and 4m again during the 3rd second. Its acceleration is therefore.. a. 1m/s squared b. 0 m/s squared c. 8 m/s squared. d. increasing. e. more than 10 m/s squared
acceleration= change in velocity/time interval b. 0 m/s squared
a force is a pair because it has both _____ and ______ counterparts
action and reaction
When you stand at rest on a pair of bathroom scales the readings on the scales will always
add up to your weight
a job is done slowly while an identical job is done quickly. The job done quickly requires more a. energy b. power c. both energy and power d. none of these
b. power
the weight of a 6kg salami is about a. 06 N b. 6.0 N c. 60 N d. 600 N
c. 60 N 6kg * 10 m/s^2
If you exert 450 J in 50 s your power output is a. 45 W. b. 3 W c. 2 W. d. 9 W.
d. 9 W. 450/ 50 = 9 1 Watt= 1 joule per 1 second
your weight is a. the gravitiational attraction between you and the universe. b. actually your mass c. the gravitational attraction between you and the universe d. dependent on your mass e. none of these. f. all of these
d. dependent on your mass
The hang time (time off the floor in an unassisted jump) of professional basketball players is typically a. 2 seconds. b. more than 2 seconds. c. 1 second. d. less than 1 second.
d. less than 1 second
the amount of inertia a certain body possesses depends on the body's a. weight b. velocity c. acceleration d. mass
d. mass
IF the mass of the earth somehow decreased with no decrease in radius, your weight would.. a. increase also b. decrease c. stay the same.
decrease
If an object's mass is increasing while a constance force is applied to the object, the acceleration ...
decreases
Consider molecules of hydrogen gas and heavier molecules of oxygen gas that have the same kinetic energy. The molecules with greater speed are the hydrogen oxygen same
hydrogen more mass does not mean more speed for the same KE less mass for the same amount of KE means more speed
A cannon with a long barrel fires a shell faster because the shell experiences more Impulse only Work only Impulse and work None of these.
impulse and work both impulse and work increase with time and distance
As a falling object gains speed, the amount of air resistance it encounters
increases More speed means more air impact.
Density is the ratio of
mass to volune
When hitting either or a wall or a haystack.. your __________ decreases by the same amount
momentum
According to Newton the lesser the distance between masses of interacting objects the [more/less] gravitational force between them
more gravitational force between them
free fall
motion under the influence of gravitiational pull only
Momentum
product of the mass of an object and its velocity
Force
push or pull
impulse
quantity force x time interval impulse = change in momentum the greater the impulse exerted on something the greater will be its change in momentum Ft = change in mv [momentum]
the mass of an object on the moon is the [same/different] on the Earth
same
Net force
the combination of all forces that act on an object
newton
the scientific unit of force
Power
the time rate of work [rate at which energy is expended] Power= work/ time
Consider two waterfalls, one twice the height of the other. The kinetic energy of each kilogram of water falling to the bottom of the taller waterfall is about twice as much. four times as much. the same.
twice as much think of the conservation of energy law. The water in the taller waterfall has twice the original potential energy.
Joule
unit of energy and work equivilant to a newton*meter
Why do objects of different weights fall at the same speed.
Because force [weight] is directly proportional to mass which means acceleration due to gravity will always stay the same.
as an object freely falls a. velocity decrease. b. acceleration increases c. velocity increases d. none of these
c. velocity increases
If a dolphin leaps out of the ocean straight up in the air, at the top of its path its speed is zero and its acceleration is
g This is in accord with Newton's second law: a = mg/m = g, everywhere along the path when air resistance doesn't interfere.
A massive, fast-moving car collides head on with a light, small-moving car. The acceleration is greater on the
small car for the same force on less mass means greater acceleration.
Speed
the distance traveled per unit of time
weight
the force of gravity on an object. The gravitational force with which a body presses against a supporting surface.
Work
The product of the force and the distance through which the force moves W= Fd
in each second of fall the distance a freely falling object will fall is .. a. about 5m b. about 10 m c. increasing d. the same
c. increasing.
the two measurements necessary for calculating velocity are..
distance and time v=d/t
whenever the net force on an object is zero, its acceleration..
is zero
a car has a mass of 1000 kg and accelerates at 1 m/s^. What is the magnitude of the force exerted on the car? a. 500 N b. 1000 N c. 1500 N d. 2000 N
b. 1000 N
support force
the force that supports an object against gravity; often called the normal force
Superman throws a boulder in space with 10 times as much mass as himself. If the boulder leaves his hands at 100 km/h, how fast does Superman recoil? 1,000 km/h 10 km/h The same speed, 100 km/h None of these are correct.
1,000 km/h law of conservation of momentum
If a car increases its velocity from 0-60 km/h in 5s, its acceleration is
12 km/h * s acceleration= change in velocity/ time interval
A 50-kg skateboarder pushes on a wall with 25 N of force. How hard does the wall push on her, and how much acceleration does she experience?
25 N and an acceleration of 0.5 m/s2. Newton's second law states that a = F/m = 25 N/50 kg
Terminal Speed
The speed at which the acceleration of a falling object terminates when air resistance balances weight
Work-energy theorem
The work done on an object equals the change in KE of the object Work= KE
A rifle of mass 1 kg is suspended by strings. The rifle fires a bullet of mass 1/100 kg at a speed of 400 m/s. The recoil velocity of the rifle is about a. 4 m/s. b. 0.01 m/s. c. 0.1 m/s. d. 1 m/s. e. none of these
a. 4 m/s Conservation of momentum momentum= mass x speed[or velocity] initial momentum of gun and bullet = final momentum of gun and bullet 0+0 = 1kg [v] + 1/100kg[400 m/s]
to produce the maximum increase in momentum of something,
apply the greatest force and extend the time of application
The average speed of a horse that gallops a distance of 10km in 20min is ... a. 10 km/h b. 20 km/h c. 30 km/h d. more than 30 km/h
avg speed= total distance/ travel time
If you exert a horizontal 100-N force on a crate and it slides along a factory floor at constant speed, then the friction between the crate and the floor is a. somewhat less than 100 N. b. 100 N. c. somewhat more than 100 N. d. a value that can't be known for certain, only guessed.
b. 100N bc the sum of all F= 0
A 30-kg girl and a 60-kg boy face each other on friction-free roller blades. The girl pushes the boy, who moves away at a speed of 1.0 m/s. The girl's speed is a. 0.45 m/s. b. 2.0 m/s. c. 0.83 m/s. d. 1.2 m/s.
b. 2 m/s girls mass x speed = boys mass x speed 30kg[s] = 60kg[1] s= 2
If a 150 lb. person steps on a pair of bathroom scales and leans so that the reading on one scale is 75 lbs., the reading on the other scale is a. 60 lbs. b. 75 lbs. c. less than 40 lbs. d. 100 lbs.
b. 75 lbs
Starting from rest, the distance a freely falling object will fall in 10seconds is about... a. 10 m b. 50 m c. 500 m d. 1000 m
c. 500m d=.5 x g x tsquared g= 9.8 m/s squared t= time squared
a light object is dropped a second earlier than a heavier object is dropped. The heavier object reaches teh ground 10m below a. sooner than the heavier object b. at the same time as the lighter object c. later than the lighter object
c. later than the lighter object
A freight train rolls along a track with considerable momentum. If it has three times as much mass, and three times as much speed, its momentum is a. zero b. doubled c. nine times as much d. unchanged
c. nine times as much
In his experiments with inclined planes, Galileo discovered that rolling balls gained equal a. accelerations in equal times. b. accelerations and equal speeds in equal times. c. speeds in equal times. d. amounts of distances in equal times.
c. speeds in equal times.
The force required to support an object in a gravitational field is equal to a. zero b. the mass of the object c. the weight of the object. d. the force required to stop it e. none of these
c. the weight of the object
before a falling object has reached its terminal velocity, its acceleration is
constant
If you toss a ball upward at 50 m/s and air resistance is negligible, the total time of the ball in air is a. 15 seconds. b. 5 seconds. c. more than 15 seconds. d. 10 seconds.
d. 10 seconds The ball loses speed at 10 m/s, which means that it takes 5 seconds to get to the top, and another 5 seconds to come down.
When a rifle is fired, it recoils so both the bullet and rifle are set in motion. The rifle and bullet ideally acquire a. equal but opposite amounts of momentum. b. kinetic energy. c. velocity d. all of these
d. all of these
a rock thrown straight upward gets to the exact top of its path. A second later its velocity is a. zero and its acceleration is zero b. zero and its acceleration is about 10 m/s^ c. about 100 m/s and its acceleration is about 10 m/s^ d. about 10 m/s and its acceleration is about 5 m/s^2 e. about 10 m/s and its acceleration is about 10 m/s ^2
e. about 10 m/s and its acceleration is about 10 m/s ^2
A feather and coin dropped in a vaccuum fall with equal a. impact times b. impact speeds c. accelerations d. kinetic energies e. all of these, except kinetic energies.
e. all of these, except for kinetic energies
A hawk gains speed when it encounters wind from behind and loses speed when it encounters wind head on. When she encounters wind at right angles to her motion, her speed relative to the ground below
increases The hawk's velocity is the resultant of air speed and wind speed. At right angles, the resultant is greater than either air or wind speed alone.
Friction
the resistive force that opposes the motion or attempted motion of an object through a fluid or past another object with which it is in contact.
Kilogram
The unit of mass. One kilogram is the mass of 1 liter of water at degrees Celsius
Equilibrium Rule
The vector sum of forces acting on a non accelerating object equals zero.
Conservation of momentun
In the absence of an external force, the momentum of a system remains unchanged. Hence, the momentum before an event involving only internal forces, is equal to the momentum after after the event.
A team of four bobsledders push their sled along a track. After their initial sprint, two of the members jump in the sled, and twice as much net force acts on it. If the acceleration remains the same, what is a reasonable explanation for the increase in force?
The mass of the cart doubled when the force doubled. The extra weight of the bobsledders in the sled causes the acceleration to remain the same, although the force is twice as great. This is in accordance with Newton's second law.
Mass
The quantity of matter in an object. More specifically, mass is a measure of the inertia or sluggishness that an object exhibits in response to any effort made to start it, stop it, deflect it, or change its state of motion in any way.
Acceleration
The rate at which velocity changes with time; the change in velocity may be in magnitude or in direction [or both]. It is usually measured m/s^2 Acceleration= change in velocity/ time interval
The muzzle velocity of a certain gun is 100 m/s. Neglecting air resistance, at the end of 1s a bullet fired straight up in the air will have traveled a distance of about.... a. 90 m b. 95 m c. 100 m d. 5 m e. none of these
b. 95 m d= .5x [9.8] x [t^2]
A mack truck and a Volkswagen traveling at the same speed have a head on collision. The vehicle to undergo the least change in velocity will be the. a. volkswagen b. Mack truck c. same for both
b. Mack truck velocity= distance/time
disregarding air resistance, objects fall at constant a. velocity b. acceleration c. increase in acceleration d. distances each successive second
b. acceleration.
Two objects move apart from each other in space. As they move apart from each other their velocities... a. increase b. decrease c. remains constant
b. decrease.
A rocket accelerates as it travels because a. the applied force on the rocket increases as buring of fuel progresses b. of its applied thrust c. the mass of the rocket decreases as fuel is burned.
b. its applied thrust
Which requires more work: lifting a 50-kg sack vertically 2 m or lifting a 25-kg sack vertically 5 m? a. lifting the 50-kg sack b. lifting the 25-kg sack c. Both require the same amount of work.
b. lifting the 25-kg sack work= force x distance