Physics test #4
what does it mean to say that momentum for any quantity is conserved?
It means momentum does not change.
What will be the kinetic energy of pile driver ram when it undergoes a 10 kg decrease in potential energy?
10 kJ
Can a machine multiply input force? Input distance? Input energy?
Force and distance, but not energy
in what sense does the moon fall
It falls away from the straight path that it would follow if there were no forces acting on it.
When the speed of a moving car is doubled, how much more kinetic energy does it have?
It has four times as much
what is recycled energy
Reused energy that otherwise would be wasted
If an object's KE is zero, what is its momentum?
Zero KE means zero speed, so momentum is also zero.
effiency
the percentage of the work put into a machine that is converted into useful work output more generally useful energy output divided bu total energy input
impulse
the product of the force acting on an object and the time during which its acts force x time force is applied IMP=FT impulse=change in momentum
work
the product of the force and the distance moved bu the force: w=fd more generally work is the components of force in the direction of motion times the distance moved
Momentum
the product of the mass of an object and its velocity (faster you go more momentum you have)
energy
the property of a system that enables it to do work
consider hitting a baseball with a bat. If we call the force on the bat against the ball the action force, identify the reaction force.
the reaction force is the force of the ball against the bat
a lunar vehicle is tested on earth at a speed of 10km/h when it travels as fast on the moon is it momentum more less or the same?
the same
power
the time rate of work power= work done/time interval more generally power is the rate at which energy is expended.
work energy theroem
the work done on an object equals the change in the kinetic energy of the object work=(triangle)KE
neap tides
tides that occur when the moon is midway between new and fi;; ion either direction tides die to the su and the moon partly cancel making the high tides lower than average and the low tides higher than average.
If you throw a ball horizontally while standing on roller skates you roll backward with a momentum that matches that of the ball will you roll backwards if you go through the motions of throwing the ball but don't let go of it?
total momentum stays constant, so no movement will occur
when is energy more evident
when it is changing
is it correct to say that if no net impulse is exerted on a system then no change in momentum of the system will occur?
yes, always
mechanical energy
energy due to the position of something or the movement of something
potential energy
energy that something possesses because of its position
Consider a baseball player batting a ball. (a) Identify the action-reaction pairs when the ball is being hit and (b) while the ball is in flight.
(a) Action; bat hits ball. Reaction; ball hits bat.(b) While in flight there are two interactions, one with the Earth's gravity and the other with the air. Action: Earth pulls down on ball (weight). Reaction: ball pulls up on Earth. And, action: air pushes ball, and reaction: ball pushes air.
If the forces that act on a cannonball and the recoiling cannon from which it is fired are equal in magnitude, why do the cannonball and cannon have very different accelerations?
-the cannon has more mass than that of the cannonball making its acceleration less
Consider the system of a single football. If you kick it, is there a net force to accelerate the system? If a friend kicks it at the same time with an equal and opposite force, is there a net force to accelerate the system?
-yes; the net force is provided by contact with your foot. If two opposite and equal forces act on the ball, the net force on it is zero and it will not accelerate
Suppose a ball of putty moving horizontally with 1 kg·m/s of momentum collides with and sticks to an identical ball of putty moving vertically with 1 kg·m/s of momentum. What is the magnitude of their combined momentum? what is the total momentum of the balls of putty before and after collision
1.41 kg·m/s 1.41 kg·m/s before and after.
Two automobiles, each of mass 1000kg, are moving at the same speed, 20m/s, when they collide and stick together. In what direction and at what speed does the wreckage move if one car was driving north and one south? or if one car was driving north and the other east?
10 m/s north
what is the efficiency of a machine that miraculously converts all the input energy to useful output energy
100%
The second floor of a house is 6 m above the street level. How much work is required to lift a 300-kg refrigerator to the second-story level?
41. Work = ΔE = Δmgh = 300 kg × 10 N/k × 6 m = 18,000 J.64
what is the momentum of a 50kg-carton that slides at 4 m/s across an icy surface
50kg x 4m/s= 200kg m/s
If an input of 100 J in a pulley system increases the potential energy of a load by 60 J, what is the efficiency of the system?
60%
what is the momentum of an 8kg bowling ball rolling at 2m/s?
8kg x 2m/s= 16kg m/s
Why does a baseball catcher's mitt have more padding than a conventional glove?
A baseball catcher's mitt contains more padding than a conventional glove in order to increase the time of collision. Greater is the padding, greater is the time of collision (time taken by ball to come to rest after collision). It reduces the amount of force applied on the hand.
Which undergoes the greatest change in momentum (if all of the baseballs have the same speed just before being caught and just after being thrown)? which has the greater impulse
A baseball that is caught and then thrown back
machine
A device, such as a lever or pulley, that increases (or decreases) a force or simply changes the direction of a force.
inverse-square law
A law that relates the intensity of an effect to the inverse square of the distance from the cause. Gravity follows an inverse-square law, as do the effects of electric, magnetic, light, sound, and radiation phenomena.
scalar quantity
A physical measurement that does not contain directional information
drop a stone from the top of a high cliff identify the system in which the net momentum is zero as the stone falls
A stone is dropped from the top of a high cliff. If we consider the system the stone + Earth, then its initial momentum is zero and no external force acts on it as the stone falls. So the momentum of the system is zero as the stone falls.
when you jump from a significant height why is it advantageous to land with your knees slightly bent?
According to the Impulse momentum theory, bending your knees will prolong the amount of time that the force of impact is applied.
in terms of impulse and momentum why do air bags in cars reduce the risk of injury in an accident
Air bags increase the time the force is applied and decrease the force, so the result is a lesser force for a longer duration
exactly what is it that enables an object to do work?
Any object that possesses mechanical energy - whether it is in the form of potential energy or kinetic energy - is able to do work. That is, its mechanical energy enables that object to apply a force to another object in order to cause it to be displaced.
many years ago automobiles were manufactured to be as rigid as possible whereas todays autos are designed to crumple upon impact why?
Crumpling increase the time to reduce the momentum of a car, resulting in less impact on the people inside
law of conservation of energy
Energy cannot be created or destroyed; it may be transformed from one form into another, but the total amount of energy never changes
which team wins in a tug of war the team that pulls harder on the rope or the team that pushes harder in the ground
Explain. The winning team pushes harder against the ground. The ground then pushes harder on them, producing a net force in their favor
if you toss a ball upward is the momentum of the moving ball conserved is the momentum of the system consisting of ball + earth conserved?
For just the ball, momentum changes and is not conserved; for the larger system momentum is conserved due to the forces acting being only internal
betty (mass 40kg) standing on slippery ice, catches her leaping dog (mass 15kg) moving horizontally at 3.0m/s show that the speed of betty and her dog after the catch is about 8.0m/s
From the conservation of momentum,Momentumdog = momentumJudy + dog(15 kg)(3.0 m/s) = (40.0 kg + 15 kg)v45 kgm/s = (55 kg)vv= 0.8 m/s
A car carrying a 75-kg test dummy crashes into a wall at 25 m/s and is brought to rest in 0.1 s. Show that the average force exerted by the seat belt on the dummy is 18,750 N.
Ft =△mvF =△mv/t
is the force of gravity stronger on a piece of iron than on a piece of wood of the same mass? defend your answer.
If both have the same mass, then the force of gravity from the Earth would be the same on each of them, since force of gravity depends on mass and distance, and distance would remain the same.
what does the work energy theorem say about the speed of a satellite in circular orbit
In accord with the theorem, once moving, no work is done on the satellite (because the gravitational force has no component parallel to motion), so no change in energy occurs. Hence the satellite cruises at a constant speed.
you jump from a canoe to the nearby dock expecting an easy landing instead you land in the water what is your explanation for this mishap?
In jumping, you impart the same momentum to both you and the canoe. This means you jump from the canoe that is moving away from the dock which reduces your speed to the dock so you don't jump as far as you expected to.
Law of Conservation of Energy
In the absence of and 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 the event: Or, mv(before the event) = mv(after the event)
explain how a swarm of flying insects can have a net momentum of zero
In this case, the swarm as a whole appears to remain in the same place. Any non-zero net momentum in any direction causes the swarm to fly in that direction.
what is the relationship between force and distance in an inverse law
Inverse relationships are common in nature. In electrostatics, the electrical force between two charged objects is inversely related to the distance of separation between the two objects. Increasing the separation distance between objects decreases the force of attraction or repulsion between the objects.
compared with a car moving at some original speed how much work must the brakes of a car supply to stop a car that is moving twice as fast? How will the stopping distance compare?
It takes four times the work and four times the stopping distance.
When you are struck by a moving object, is it favorable that the object makes contact with you over a short time or over a long time?
Long contact time decreases the magnitude of the average force and is favorable.
a 2-kg ball of putty is moving to the right has a head on inelastic collision with a 1-kg putty ball moving to the left. If the combined blob doesn't move just after the collision what can you conclude about the relative speeds of the balls before the collision?
Momentum after collision is zero, which means the net momentum before the collision was zero. So, the 1 kg ball must be moving twice as fast as the 2 kg ball so that the magnitudes of the momenta are equal. The 1 kg ball had momentum equal to the momentum of the 2 kg ball prior to the impact
would the springs inside a bathroom scale be more compressed or less compressed if you weighed yourself in an elevator that was acceleration upward? downward?
More compressed going up. Less compressed going down.
which requires more work stretching a strong spring a certain distance or stretching a weak spring the same distance
More force is required to stretch the strong spring, so more work is done in stretching it the same distance as a weaker spring.
which requires more work lifting a 50kg sack a vertical distance of 2 m or lifting a 25-kg sack a vertical distance of 4m?
Neither, they are the same
When you rub your hands together, can you push harder on one hand than the other?
No, for each hand pushes equally on the other in accord with Newton's third law- you cannot push harder on one hand than the other.
can you produce a net impulse on an automobile if you sit inside and push on the dashboard? Can the internal forces within a soccer ball produce an impulse on the soccer ball that will change its momentum?
No, never.
can we correctly say that hydrogen is a new source of energy why or why not?
No. It takes energy to make hydrogen.
if two objects have equal kinetic energies do they necessarily have the same momentum
Not at all. For two objects of the same KE, the one of greater mass has greater momentum. (The mathematical relationship is p2 = 2m x KE.)
comment on whether or not the following label on a consumer product should be a cause of concern CAUTION: the mass of this product pulls on every other mass in the universe with an attracting force that is proportional to the product of the masses and inversely proportional to the square of the distance between their centers.
Nothing to be concerned about on this consumer label. It simply states the universal law of gravitation, which applies to all products, It looks like the manufactuerer knows some physics and has a sense of humor.
what is the ultimate source of geothermal energy
Nuclear power in Earth's interior
in terms of impulse and momentum why do mountain climbers use nylon ropes which stretch considerably under tension?
Nylon ropes are elastic ropes which would lengthen the amount of time that the force is applied thus would help prevent injuries for mountain climbers.
is gravitational force acting on a person who falls off a cliff? on an astronaut inside an orbiting space shuttle
On an astronaut inside an orbiting space shuttle? Gravitational force is indeed acting on a person who falls off a cliff, and on a person in a space shuttle. Both are falling under the influence of gravity.
If you drop an egg from shoulder height onto a pillow, the egg will not break. However, if you drop an egg onto a tile floor, the egg will break. Why do we have different results?
Once again, look at the relationship Ft = Δmv. Since the change in momentum (right hand side of equation) is the same in both cases, then if "t" is large, the "F" is small. Similarly, if "t" is very small, the "F" is very large, and the egg is broken.
in terms of impulse and momentum why do padded dashboards make cars safer?
Padded dashboards make automobiles safer because it will increase the time required to stop your head from moving forward during an accident. The increased stopping time results in a smaller force being applied to the person's head.
You hold an apple over your head. (a) Identify all the forces acting on the apple and their reaction forces. (b) When you drop the apple, identify all the forces acting on it as it falls and the corresponding reaction forces. Neglect air drag.
Part A The acting force on the apple is that it is pulled down by Earth, therefore the reaction is the apple pulling up on the Earth. So when the hand pushes the apple upward (action) the apple pushes the hand downward (reaction).Part B The apple is in free fall and the only force acting on it is its weight pulling it down.
how many watts of power do you expend when you exert a force of 50N that moves a crate 8m in a time interval of 4s?
Power = Fd/t = (50N)(8m)/(4s) = 100J/1s = 100 watts
If you stand next to a wall on a frictionless skateboard and push the wall with a force of 40 N, how hard does the wall push on you? If your mass is 80 kg, show that your acceleration is 0.5 m/s2.
Pushing the wall is the force of "action". The wall reacts by applying a force of 40 Nto you in the opposite direction. Since you are standing on a skateboard, the force offriction is negligible. The only force (in the horizontal direction) acting on you is the 40 N force of reaction of the wall. Now we can apply the second law to calculate theacceleration. a=f/m a=40N/80kg= .5 m/s2
calculate the resultant of a horizontal vector with a magnitude of 4 units and a vertical vector with a magnitude of 3 units
Resultant = √(42 + 32) = 5. This is the hypotenuse of a 3-4-5 right triangle.
why is it advantageous to roll with the punch in boxing?
Rolling with the punch increases contact time, which decreases the force
how does speed affect the friction between a road and a skidding tire
Speed has no effect on the friction.
On a playground slide, a child has potential energy that decreases by 1000 J while her kinetic energy increases by 900 J. What other form of energy is involved, and how much?
The 100 J of potential energy that doesn't go into increasing her kinetic energy goes into thermal energy—heating her bottom and the slide.
At what point in its motion is the KE of a pendulum bob at a maximum? At what point is its PE at a maximum? When its KE is at half its maximum value, how much PE does it have relative to its PE at the center of the swing?
The KE of a pendulum bob is maximum where it moves fastest, at the lowest point; PE is maximum at the uppermost points. When the pendulum bob swings by the point that marks half its maximum height, it has half its maximum KE, and its PE is halfway between its minimum and maximum values. If we define PE = 0 at the bottom of the swing, the place where KE is half its maximum value is also the place where PE is half its maximum value, and KE = PE at this point. (By energy conservation: Totalenergy = KE + PE.)
what is the ultimate source of energy for fossil fiels dams and windmills
The Sun
is the acceleration due to gravity more or less atop Mt. Everest than at sea level defend your answer.
The acceleration due to gravity is greater at sea level.
Why is a force that is applied for a short time more effective in karate?
The average force is increased.
if you were in a car that drove off the edge of a cliff why would you be momentarily weightless would gravity still be acting on you
The car no longer acts as a "support force". Both you and the car are in free fall and gravity is still acting on you as evidenced by ur acceleration toward the ground.
A car is raised a certain distance in a service-station lift, thus giving it potential energy relative to the floor. If it were raised twice as high, how much more potential energy would it have?
The car with twice the mass has twice the potential energy.
If a ball is projected upward from the ground with 10 kg m/s momentum, what is the momentum of recoil of the world? Why do we not feel this?
The change of momentum of the Earth will be equal and opposite: 10 kg m/s.
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?
The energy is kinetic energy before it hits the ground; it is thermal energy after.
how does the force of gravity between two bodies change when the distance between them is doubled?
The force decreases to ¼ of its initial value.
is the force of gravity stronger on a crumpled pierce of paper than on an identical piece of paper that has not been crumpled defend your answer.
The force of gravity is the same on each because the masses are the same, as Newton's equation for gravitational force verifes.
if a mack truck and a mini cooper have a head on collision which vehicle experiences the greater force of impact? the greater impulse> the greater change in momentum? the greater deceleration?
The force of impact is the same.The impulse is the same.The change in momentum is the same.The minicooper with lower mass will experience greater deceleration
If you exert a horizontal force of 200 N to slide a crate across a factory floor at constant velocity, how much friction is exerted by the floor on the crate? Is the force of friction equal and oppositely directed to your 200-N push? If the force of friction isn't the reaction force to your push, what is?
The friction on the crate is 200N, which cancels your 200N push on the crate to yield the zero net force that accounts for the constant velocity (zero acceleration). Although the friction force is equal and oppositely directed to the applied force, the two do not make an action-reaction pair of forces. That's because both forces do act on the same object--the crate. The reaction to your push on the crate is the crate's push back on you. The reaction to the frictional force of the floor on the crate is the opposite friction force of the crate on the floor.
an apple falls because of gravitational attraction to earth. How does the gravitational attraction of earth to the apple compare?
The gravitational attraction of the Earth to the apple is identical to the gravitational attraction of the apple to the Earth.
your friend says that the law of momentum conservation is violated when a ball rolls down a hill and gains momentum what do you say?
The law of momentum conservation says that IF there are no external forces acting on the system, momentum will not change. Since, gravity, an external force, affects the ball, it is not a violation of the law when the ball gains momentum.
why do 8 ounce boxing gloves hit harder than 16-ounce gloves?
The lighter gloves have less padding, and less ability to extend the time of impact, and therefore result in greater forces of impact for a given punch.
what would be the path of the moon if somehow all gravitational forces on it vanished to zero
The moon would move in a straight-line path instead of circling both the Sun and Earth.
Which has a greater momentum: a heavy truck at rest or a moving skateboard?
The moving skateboard.
When the mass of a moving object is doubled with no change in speed, by what factor is its momentum changed? Its kinetic energy?
When the mass is doubled with no change in speed, both momentum and KE are doubled.
when is the potential energy of something significant?
When the potential energy changes
Railroad car A rolls at a certain speed and makes a perfectly elastic collision with car B of the same mass. After the collision, car A is observed to be at rest. How does the speed of car B compare with the initial speed of car A? If the equally massive cars of the preceding question stick together after colliding inelastically, how does their speed after the collision compare with the initial speed of car A?
The speed of car B is equal to the initial speed of A. Their speed is half the initial speed of car A.
does the spring that supports a pendulum bob work on the bob as its swing to and fro? does the force of gravity do any work on the bob
The string tension is everywhere perpendicular to the bob's direction of motion, which means there is no component of tension parallel to the bob's path, and therefore no work done by the tension. The force of gravity, on the other hand, has a component parallel to the direction of motion everywhereexcept at the bottom of the swing, and does work, which changes the bob's KE.
what two forces act on you while are you in a moving elevator? When are these forces of equal magnitudes and when are they not?
The two forces are the normal force and mg, which are equal when the elevator doesn't accelerate, and unequal when the elevator accelerates.
conservation of energy
The work output of any machine cannot exceed the work input. In an ideal machine, where no energy is transformed into thermal energy
parallelogram rule
To find the resultant of two non-parallel vectors, construct a parallelogram wherein the two vectors are adjacent sides. The diagonal of the parallelogram shows the resultant.
how can a fully dressed person at rest in the middle of a pond on perfectly frictionless ice get to shore?
To get to shore, a person may throw clothing or something so the momentum of what is thrown will send the thrower in the oppsite direction. You will recoil towards the shore
why cant a superball released from rest reach its original height when it bounces form a rigid floor?
When a Superball hits the floor some of its energy is transformed to heat. This means it will have less kinetic energy after the bounce than just before and will not reach its original level.
When a rifle with a longer barrel is fired, the force of expanding gases acts on the bullet for a longer distance. What effect does this have on the velocity of the emerging bullet? (Do you see why long-range cannons have such long barrels?)
When a rifle with a long barrel is fired, more work is done as the bullet is pushed through the longer distance. A greater KE is the result of the greater work, so of course, the bullet emerges with a greater velocity. (Note that the force acting on the bullet is not constant, but decreases with increasing distance inside the barrel.)
if you drop a rubber ball on the floor it bounces back up. What force acts on the ball to provide the bounce
When the ball exerts a force on the floor, the floor exerts an equal and opposite force on the ball- hence bouncing. The force of the floor on the ball provides the bounce.
When you catch a fast-moving baseball with your bare hand, a good idea is to catch it so that your hand stops it
When you catch a fast-moving baseball with your bare hand, a good idea is to catch it so that your hand stops it
Newton's 3rd Law of Motion
Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first. to every action there is always an opposed equal reaction -2 objects
if you were in a freely falling elevator and you dropped a pencil it would hover in front of you is there a force of gravity acting on the pencil?
Yes because if you were in free fall in an elevator, then you, the elevator and the pencil will be accelerated downward by gravity. Since a pencil has mass and F=ma and it is experiencing gravitational acceleration, there is a gravitational force on the pencil.
does the international space station have gravitational PE KE
Yes to both, relative to Earth, because work was done to lift it in Earth's gravitational field and to impart speed to it.
Consider the two forces acting on a person who stands still, namely the downward pull of gravity and the upward support of the floor. Are these forces equal and opposite? Do they comprise an action-reaction pair? Why or why not?
Yes, they are the only forces acting on a non accelerating person; no they are 2 interactions - person-earth and floor-person.
why do you do not work on a 25kg backpack whne you walk horizontal distance of 100m
You do no work because you haven't exerted more than a negligible force on the backpack in the direction of motion. Also, the energy of the backpack hasn't changed. No change in energy means no work done.
you watch your friend take off in a jet plane and you comment on the kinetic energy she has acquired but she says she experiences no such increase in kinetic energy who is correct?
You're both correct, with respect to the frames of reference you're inferring. KE is relative. From your frame of reference she has considerable KE for she has a great speed. But from her frame of reference her speed is zero and KE also zero.
if your friend pushes a lawnmower four times as far as you do while exerting only half the force which one of you does more work? How much more
Your friend does twice as much work (4 x 1/2 > 1 x 1).
inelastic collision
a collision in which objects become distorted, generate heat and possibly stick together.
elastic collision
a collision in which objects rebound without lasting deformation or the generation of heat.
black hole
a concentration of mass that results form a gravitational collapse near which gravity is so intense that not even light can escape.
vector quantity
a quantity that has both magnitude and direction
lever
a simple machine consisting of a rigid rod pivoted at a fixed point called the function
forces of 3.0N and 4.0N act at right angles on a block of mass 2.0 kg. Show that the acceleration of the block is 2.5m/s^2
a=F/m, 5.0 N/2.0 kg = 2.5 m/s^2. The resultant vector of the 3.0 N and 4.0 N vectors is 5.0.
Vector
an arrow that represents the magnitude and direction of a quantity
if you apply force on an object like the wall the wall is
applying force back
Suppose, from the same height (5 meters), we drop a lump of clay and a perfect golf ball of equal masses. (The mass of each is 0.05 kilograms.) The two will reach the floor
at the same time and with the same velocity
Why do both the sun and the moon exert a greater gravitational force on one side of the Earth than the other?
because of the distance between the sun or moon and the earth is different for the near and far sides. The near side will feel a greater pull of gravity than the far side.
weightless
bring without a support fore as in free fall
kinetic energy
energy that something possesses because of motion quantified bu the relationship kinetic energy=1/2mv^2
, Whenever one object exerts a force on a second object, the second object exerts an ________ and opposite force on the first.
equal
state newtons law of universal gravitation in words then do the same with one equation
every body attracts every other body with a force that, for any two bodies, is directly proportional to the product of their masses and inversely proportional to the square of the distance separating them.F = m1m2/d2
law of universal gravitation
every body in the universe attracts every other body with a force that for two bodies is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers f=g m1m2/d2
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?
exert the greatest force over the longest time.
cite an example in which a force is exerted on an object without doing work on the object
force is needed to hold a barbell overhead, but this force does no work on the barbell while the bar bell is at rest. ... Power for each is the same because the same work is done in the same time.
It only makes sense that the longer we apply a force (i.e. make t large), the ________ the final velocity.
greater
spring tides
high or low tides that occur when the sun, earth, moon are all lined up so that the tides due to the sun and the moon coincide making the high tides higher than average and the low tides lower than average
why is it difficult for a firefighter to hold a hose that ejects large amounts of water at a high speed?
hose tends to recoil from theejected water
Impulse-momentum relationship
impulse is equal to the change in the momentum of the object that the impulse acts on.
Larry weighs 300 N at the surface of earth what is the weight of earth in the gravitational field of Larry?
in accord with Newton's 3rd law, the weight of the Earth in the gravitational field of the apple is 1 N; the same as the weight of the apple in the Earth's gravitational field.
law of conservation of momentum
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 the event. mv(before the event)=Mv( after event)
what are the two ways to increase impulse?
increasing the force or increasing the time interval.
how does the thickness of paint sprayed on a surface change when the sprayer is held twice as far away?
it is 1/4 the thickness of the closer distance. Inversesquarelaw (1/22 = 1/4 )
Momentum is directly proportional to
mass times velocity
Momentum formula
momentum=mass*velocity
components
mutually perpendicular vectors, usually horizontal and vertical, whose vector sum is a given vector
Calculate the resultant of the pair of velocities 100 km/h north and 75 km/h south. Calculate the resultant if both of the velocities are directed north. resultant of two vectors at right angles to each other
north 100+-75=25, 100+75=175 north, the difference is the second vector.
Suppose the speed the two objects at the moment of impact is 10 meters per second (10 m/s). When the two strike the floor, the lump of clay sticks to the floor, and the perfect golf ball bounces back up with the _____________ speed as it struck the floor What is the change in momentum of the lump of clay?
same speed The clay is traveling at 10 m/s at the moment of impact, but is stopped almost immediately (speed = 0). The difference in speed is 10 m/s - 0 m/s = 10 m/s. Therefore, the change in momentum is Δmv = 10 kg x 10 m/s = 100 kg m/s.
When you push against a wall with your fingers, they bend because they experience a force. Identify this force.
the force of the wall pushing back on your fingers
weight
the force that an object exerts on a supporting surface or if suspended on a supporting rope which is often but not always due to the force of gravity.
How does a helicopter get its lifting force?
the helicopter gets its lifting force by pushing air downward, in which case the reaction is the air pushing the helicopter upward
gravitational field
the influence that. a massive body extends into the space around itself producing a force on another massive body. it is measured in newtons per kilogram
When a cannonball is fired, the momentum of the system (cannon + cannonball) is conserved. Would momentum be conserved for the system if momentum were not a vector quantity?
the momentum of the cannon is equal to the magnitude of the momentum of the cannon ball and points in the opposite direction.
