Physics midterm/final
Define heat
The transfer of when two objects come in contact with each other; heat flows from the hotter object to the smaller object.
What happens when the same force is applied to two objects of different masses?
They object with the the higher mass will have less acceleration, and vice versa.
A force of 35 N is applied horizontally to a 4.0 kg crate initially at rest on a horizontal frictionless surface. If the crate displaces 15 m, what would be its final velocity?
Use equation: a = Fnet/m = 8.75 m/s^2 Vf^2 = Vi^2 + 2ad
Define Displacement
Vector quantity, a change in position
Define Velocity:
Vector quantity, a change in position over time
Define Impulse
Vector quantity, product of the average force on an object divided by the time interval over which it acts.
Define Acceleration:
Vector quantity, velocity over time
How are vectors and scalars different?
Vectors have both direction and magnitude.
What formula do you use for calculating final velocity for an accelerating object as a function of time?
Vf = Vi + at
What formula do you use to find the final velocity of an object, without having time?
Vf^2 = Vi^2 + 2ad
If a non-zero net force is applied to an object, will the momentum of the object change? What else affects how much the momentum will change?
Yes; the amount of time the force is applied
Newtons First Law
Object in motion stay in motion until acted on by an equal or unbalanced floors
When are calculations rounded-off based on least precision?
During adding and subtracting
When are calculations rounded off based on significant figures?
During multiplying and dividing
What must happen for a substance to melt or vaporize? Condense or freeze?
Energy is added; energy is removed.
What is the First Law of Thermodynamics?
Energy is neither created or destroyed
Newton's Third Law
Equal Opposite Reaction
How is power computed?
P = W/t or P = Fv
A small plane has a mass of 3000 kg and accelerates at 10 m/s^2 down the runway. What formula would you use to find the magnitude of the force acting on the plane?
F = ma = 3000 kg x 10 m/s^2 = 30,000
Cart 1 has a mass of 1 kg, cart 2 has a mass of 2 kg. They are pushed apart by a spring, the spring exerts 2 N of force onto cart 1. how much force is exerted onto cart 2?
F= -2N (Newton's third law)
What is the sum of two vectors called?
Resultant vector.
Driving along one day, a giant beetle splatters against my windshield. Which is greater, the force acting on the windshield or the force acting on the beetle?
Same magnitude opposite directions.
How does water's behavior from 4 degrees to 0 degrees benefit plants and animals?
Ice becomes less dense when it expands, which prevents lakes from freezing from the bottom up each winter, and ice might never completely melt in summer.
How is impulse computed?
Impulse = (F) (Change in t)
A 50 Ns impulse is exerted on a 0.25 kg mass for 0.30 s by a 5.0 kg object. What is the change in momentum of the 0.25 kg object?
Impulse = change in momentum = 50 Ns
Change in momentum is equal to what? What is this called?
Impulse; Impulse-Momentum Theorem
Force
a push or a pull on an object
A ball of mass 0.400 kg rolls off a tabletop at a speed of 3.0 m/s. The table is 1.14 m high. Assume the potential energy at the floor is zero. Disregard any rotational energy. a. What is the total energy of the ball as it rolls off the table? b. While the ball is in the air, after it leaves the table, what happens to the relationship between it's kinetic and potential energies? c. What is the value of the kinetic energy of the ball when it strikes the floor?
a. MEi = PEi + KEi MEi = mgh + 1/2 mv^2 Answer should be: 6.27 J b. KE will go up, and PE wil go down c. MEi = MEf answer should be 6.27 J = KEf
Is thermal Energy conserved in a particular situation?
In an isolated and closed system.
A mass of exactly 5.000 kg is sitting on a flat wooden board. A spring scale is attached to the mass. A reading of 22.16 N is needed to just start to drag the mass over the board. a. What is the value of the force of static friction? b. What is the value of the normal force on the mass? c. What is the value of the coefficient of static friction?
a. f = F = 22.16 N b. N = mg = 5.000(9.8) = 49.00 N c. f/N = 22.16/49.00 = 0.45
Define Latent heat
amount of heat absorbed or released by a substance undergoing a change of state such as ice changing to water or water to steam, at constant temperature and pressure.
How fast is velocity in the y axis, of a free falling object, after 3 s?
(9.81)(3)=29.4 m/s
A 70 kg hockey player exerts a 15N force on a 62 kg hockey player for 0.3 s. What formula would you use to find out what is the magnitude of the impulse applied to the 60 kg hockey player?
(F) (Delta t) = 15(0.3) = 4.5 Ns
A runner starts from rest andd after 3.0 s is running at 4 m/s. What formula do you use to calculate the runner's average acceleration?
-(vf - vi)/t -Answer should be 1.333 repeating
A cart with a weight of 400.0 N is accelerated across a level surface at 0.75 m/s2. What net force acts on the wagon?
-First find the mass of the car: m = w/g = 40.81 -Fnet = ma = 30.6 N
A sailboat goes 1.65 km/h. How would you calculate how far it should travel in 0.7 hours?
-Multiply it's velocity by the time -You should get 1.2 km
A ball is released from rest and falls freely 8.0 m to the ground. How do you calculate the speed before impact?
-Use formula Vf^2 = Vi^2 + 2ad -Solve for Vf -Vf = 13 m/s
A rock is thrown straight upward with an initial velocity of 12.2 m/s from a location where the acceleration due to gravity is 9.81 m/s2. What formula do you use to find how high up does it go?
-Vf^2 = Vi^2 + 2ad -Use half of the d, and Vf will be 0
A Corvette accelerates at a constant rate from rest to a speed of 32.4 m/s in 7.00 s. What is the way we calculate the displacement of the Corvette in this time interval?
-d=1/2(vf+vi)t -answer should be: 113m
What formula do you use to find the displacement (change in position) of an accelerating object?
d = Vi+ 1/2at^2
A ball is released from rest and falls freely 8.0 m to the ground. What formula would you use to calculate what is the speed before impact?
-vf^2=vi^2+2ad -Where a is gravity - vf = squareroot of (vi^2 + 2ad) -Answer should be: vf=13 m/s
A plane accelerates at 20 m/s^2 from rest and lifts off the runway after 7 s. What formula would you use to calculate how far it traveled before taking off?
d=1/2at^2 Answer should be: 490
My dog has a mass of 10 kg when she stands with all four paws on the scale. What will her mass be if she stands on only her two hind legs?
10 kg
A hockey player initially skating at a velocity of 5 m/s speeds up to 8 m/s. What happens to the momentum of the hockey player?
Increases
How are static friction and kinetic friction different?
Static friction opposes intended motion; kinetic friction opposes motion.
A boat goes 8 m/s due north against a current of 3 m/s. How do you calculate the resultant velocity?
Subtract the current, the boat's going against, from the boat's velocity. (You should get 5 m/s)
If an object has more mass it has more _______
inertia
What is the SI unit for length, mass, and time, respectively?
m, kg, s
Define entropy
measure of the amount of disorder in a system
How do field forces differ from contact forces?
A contact force involves a force acting on or directly touching an object; a field force acts on objects without direct contact.
What is an action-reaction pair?
A pair of forces that have the same magnitude, opposite direction, and do not act on the same objects.
Multiplying or dividing vectors by scalars results in what?
A vector quantity
Define momentum
A vector quantity, the product of mass and velocity
How can you get a moving object to change direction?
Apply force to it.
As the temperature of a substance increases, what happens to the average kinetic energy of its molecules?
It also increases; temperature is directly proportional to the average kinetic energy.
What happens to water as it cools from 4 degrees celsius to 0 degrees
It expands and becomes less dense.
If a non-zero net force is acting on an object, what is happening to the object?
It will accelerate
When an object's speed doubles, what happens to its kinetic energy? When speed triples?
It will double, it will get nine times bigger
An open train car rolls along a track while it is being filled with sand. There is negligible friction. As a result of the accumulating sand, what happens to the speed of the train car? (Assume negligible friction and the cart is just rolling along, not receiving any additional force to regulate its speed.)
It will slow down
How is kinetic energy computed?
KE = 1/2 mv^2
What three dimensions are used to derive most measurements in physics?
Length, time, and mass.
The sum of the potential energies and the kinetic energy is called what?
Mechanical Energy
How are beginning and ending linear momentum related?
Momentum is conserved for systems, that are isolated (Fnet = 0) and closed (no mass can enter or leave the system). This is called the Law of Conservation of Momentum (pf = pi)
How is net force computed?
By adding all the forces acting on an object
How do you find speed/velocity from a position/displacement-time graph?
Calculate slope
How do you find velocity from an acceleration-time graph?
Calculate the area under the curve
How do you find displacement from a velocity-time graph?
Calculate the area under the curve.
How do you find acceleration from a speed/velocity-time graph?
Calculate the slope
What is the most important indicator of thermal energy?
Temperature
Heat flow will occur between two objects in thermal contact under what condition?
Temperature difference
What forces are shown in a free-body diagram?
The Forces acting on an object
what are the SI units for work power and energy?
The Joule (J) 1J = (1N) (m) = 1 (kg) (m^2/s^2)
Specific Heat
The amount of energy that must be added to the material to raise the temperature of a unit mass by one temperature unit.
Define Kinetic Energy
The energy associated with the motion of an object which depends on the square of the velocity
Define Gravitational potential energy
The energy associated with the position of an object in relationship to an object or point of reference. It is also the potential to work
Define elastic potential energy
The energy stored in any compressed or stretched object such as a spring, rubber band, etc.
How are impulse and momentum related?
The impulse of an object is equal to the change in momentum. It can be described by the equation (F) (Delta t) = (Delta p)
Explain why, when you jump into a pool just after the first strong cold front of the winter, the water is still very warm
The lakes are heated from the bottom by the earth, the colder denser water sinks to the bottom where it is warmed and then pushed up by the continuous flow of cooler water from the top
A 70 kg student running down the halls bumped into a 90 kg student who was running down the hall towards her. What happens to the magnitude of the momentum of the 90 kg person?
The momentum will decrease
What factors affect friction?
The normal force and the coefficient of friction (how rough the surface is).
What can affect the coefficient of friction between two surfaces? What absolutely does not affect the coefficient of friction?
The normal force, the friction force, and whether or not the object is in motion; the mass does not affect it.
In elastic collisions what is conserved?
momentum and kinetic energy
In inelastic collisions what is conserved?
momentum only
Acceleration can be a change in ____ or _____
speed, direction
Normal Force
the perpendicular contact exerted by a surface on an object
How is weight computed?
w = mg
What is the net force and what is the acceleration during equilibrium?
zero
A bird navigates 1.8 m west and 7.0 m north. How would you determine the direction and magnitude of the bird's displacement, in regards to it's original position? (Remember: when they ask for the direction, they also want the angle of said direction)
-Make a vector diagram -The resulting shape should resemble a right triangle -Use A^2+ B^2=C^2 to find the magnitude -Use SOH CAH TOA to find the angle of direction -To determine what compass direction it's going, find which of the two ORIGINAL vectors the measured angle is touching. The direction of that vector will be the last direction. (For example: if the problem says a vector was going East and the measured angle of direction was touching that vector going East, then we would say "____ of East") -You should get 7.22 m 76 degrees North of West
A plane flies from Point A to Point B. B is 1207 km west, and 957 km south of A. How do you find the magnitude and direction of the plane's displacement?
-Make a vector diagram -The resulting shape should resemble a right triangle -Use A^2+ B^2=C^2 to find the magnitude -Use SOH CAH TOA to find the angle of direction -To determine what compass direction it's going, find which of the two ORIGINAL vectors the measured angle is touching. The direction of that vector will be the last direction. (For example: if the problem says a vector was going East and the measured angle of direction was touching that vector going East, then we would say "____ of East") -Your answer should be close to 1540.35 km, 38.4 degrees South of West (depending on how you rounded)
A rock is thrown straight upward with an initial velocity of 12.2 m/s from a location where the acceleration due to gravity is 9.81 m/s2. How high up does it go?
-vf at the top is zero. -To solve take half the distance -d=(vf^2-vi^2)/2a -final answer should be: 7.59
Identify each of the following as scalar or vector: 1-mass of an object 2-volume of an object 3-number of petals on a rose 4-wind velocity 5-a cheetah's maximum speed 6-time 7-force 8-momentum
1-Scalar 2-Scalar 3-Scalar 4-Vector 5-Scalar 6-Scalar 7-Vector 8-Vector
If a freely falling object were dropped from rest and equipped with a speedometer, How would you calculate approximately what the speedometer would say after ____ seconds
9.81 x ___ seconds
What is Newton's Second Law, in words?
Acceleration is proportional to the force. It's inversely proportional to the mass of the object being accelerated. Acceleration is equal to the net force divided by the mass.
What two things must occur in order for work to be done?
An object must be displaced by a force. The force must have a component of the force that is parallel to the objects displacement times the distance the object travels.
A 30.0 kg child on roller skates, initially at rest, rolls 4.0 m down an incline at an angle of 25.0° with the horizontal. If there is no friction between the incline and the skates, what is the kinetic energy of the child at the bottom of the incline? (g = 9.81 m/s2) [Hint: Remember that this is a work/energy question!]
Change in Kinetic Energy = Work = F d cos(theta) Answer should be 497 J
What is the difference between Displacement and Distance?
Displacement uses both direction and magnitude. (5 miles NW) Distance only uses magnitude ( 5 miles)
How is Gravitational Potential Energy computed?
GPE = mgh
Define Plasma
Ionized gas
A 4.0 kg mass is dropped from a height of 15.0 m. How would you calculate to find out what will it's kinetic energy be just before it hits the ground?
MEi = MEf PEi = KEf mgh = KEf Answer should 588 m
What quantities are vectors?
Magnitude and direction.
A racquetball moving at 7 m/s hits the wall of the court and rebounds to the hitter at 7 m/s. What happened to the size of the momentum of the racquetball?
Magnitude of momentum will remain the same
What quantities are scalar?
Magnitude only
Impulse is equal to the change in an object's ____
Momentum
What is the Second Law of Thermodynamics?
Natural processes go in a direction that maintains or increases the total entropy of the universe. This means, heat flows spontaneously from hot to cold.
What is the velocity of an object from the viewpoint of another moving object?
Relative velocity
When are zeros not significant?
Terminal zeros that are merely place holders, are not significant. For example Terminal zeros in a number without an explicit decimal (100, 200, 300) or leading zeros (0.00012)
When are zeros significant figures?
Terminal zeros that aren't placeholders, are significant. for example at the right of a decimal point (10.0) and in between digits (405)
What is the Ideal Gas Law?
The Ideal Gas Law relates the variables of pressure, volume, temperature, and number of moles of gas within a closed system.
What is the SI unit for force?
The Newton (N); 1N = 1kg m/s^2
In all natural processes, what happens to entropy?
The amount of disorder increases and so does the entropy
Define Power
The rate at which work is done or energy is transferred
As the temperature of a substance increases what happens to the average spacing of it's molecules?
The spacing increases; temperature is directly proportional to the space between the molecules
What is the name given to how much thermal energy (heat) is needed to change the temperature of a given mass by a given amount?
The specific heat
Define mechanical energy, and give it's formula.
The sum of potential and kinetic energies. ME = KE + PE
In all natural processes, the entropy of the universe will move to what?
Towards disorder
Define Convection
Transfer of energy between two objects due to a change in temperature that are not in contact
Define Conduction
Transfer of energy via direct contact between two objects
What is the Work-Energy Theorem?
W = (Delta KE) = (KEf - KEi) = 1/2 m(Vf^2 - Vi^2)
How is work computed?
W = F d cos θ where θ is the angle between the force and displacement when the vectors are tail to tail.
A person mowing a lawn with a push mower exerts a force of 100 N at an angle of 30.0° above the horizontal. Sketch a picture of this situation. What formula do you use to find out how much work does he do when he moves 27.0 meters, at a constant velocity?
W = F d cos(theta) Answer should be 2340 J
How are work and potential energy related? (Think of an object that has been lifted off the ground)
Work = change in potential energy (W = (Delta PE)
How are work and kinetic energy related?
Work-Kinetic Energy Theorem
a 3.0 kg block is on a frictionless horizontal surface F1 = 10 N and pulls to the left F2 = 13 N to the right, what is the acceleration of the block?
a = Fnet/m 3N/3.0 kg= 1.0 m/s^2
Friction
a force that opposes the motion of an object
A rock is thrown horizontally with an initial velocity of 23.0 meters per second from the top of a tower 72 meters high. (g = 9.81 m/s2 and neglect air resistance). a. Calculate the initial vertical velocity b. Calculate the initial horizontal velocity c. How long does it take the rock to reach the ground? d. What is the horizontal velocity of the rock before it hits the ground? e. What is the vertical velocity of the rock just before it reaches the ground? f. What is the velocity of the rock just before it reaches the ground?
a. Viy = 0 b. Vix = 23 m/s c. Use modified formula: t= squareroot (2y/a) = 2(-72)/-9.8 = 3.8 s d. 23 m/s (horizontal velocity remains constant) e. Vfy = Viy + at = -37 m/s f. V = Squareroot(Vx^2 + Vy^2) = 1900 m/s tan^-1(37/23)=58 degrees
Identify the next part of the action/reaction pairs in the following situations: a. A volleyball player spikes the ball; b. A hammer hits a nail into a wall; c. A car smashes into mailbox;
a. ball strikes volleyball player b. nail hits hammer and wall hits nail c. mailbox smashes into car
A velocity vector with a magnitude of 25.0 m/s at a heading of 60.0° to the +x-axis a. Calculate what the x-component is? b. Calculate what the y-component is?
a. use modified trigonometry formula: adjacent(x)=hyp cos theta (should be 12.5) b. use modified trigonometry formula: opposite(y)=hyp sin theta (should be 21.7 m/s)
How is linear momentum computed?
p = mv
Net Force
the sum of the forces acting on an object
Define Work
the transfer of energy by a mechanical process
Define Radiation
transfer of energy by electromagnetic waves
