# Physics 101 Test 3

version from 2015-10-19 14:45

## Section

Gravity increases with the _ and _ of two objectsSize - Proximity
Inverse Square Relationship - DefineThe gravitational force is inversely proportional to the square root of the distance [between two objects]
If the distance between two objects is doubled than the gravitational force is _ as big1/4
Law of Universal Gravitation - Define - equationALL objects have a gravitational pull between them - F=G[(m1xm2)/(r^2)]
G in Universal Gravitation equation = 6.67x10^-11 (Newtons x meters^2)/(Kilograms^2)
The gravity between objects on earth is hardly felt because of the LARGE force of gravity exerted by the _ on each objectEarth
Geosynchronous - DefineThe distance from earth where a satellite would stay above a specific part of the earth and rotate at the SAME speed as the earth. Crazy!!
T or F. The moon orbits the earthFalse. They actually both orbit the center of mass for the "earth-moon system." The two objects have an equal and opposite pull on each other, but because earth has much more mass the center of this system is much closer to the earths center (located under the earths surface.)
Explain the Tide with the moonAs the earth and moon accelerate towards each other, the side of the earth that is CLOSER to the moon is "falling faster" (because it is closer to the moon and is therefor more affected by the gravity of the the moon; the ocean is pulled by the gravity of the moon
Does the sun affect the tide on earth? does anything else also affect it?Yes - ALL orbiting bodies have an effect on ALL other orbiting bodies
Does the land experience tidal movement?Yes!!!
Field Concept - Define - StepsDetermine the force exerted by an object and then calculate the force exerted on a second object - Step 1(an objects Mass exerts a gravitational field at every point in space) STEP2 (The second object interacts with the field created by the first by virtue of its mass)
Field - DefineA region of space that has a number of vectors assigned to every point
Linear momentum - define - equation - unitsThe product of an objects mass and its velocity - p=mv - (Kg)(m/s)
Momentum - defineHow hard it is to stop an object
T or F, a parked truck has momentumFalse, an object needs velocity to have momentum
Impulse - defineApplying a net force on an object for a certain amt of time; a change in an objects momentum
T or F, impulse is NOT a vector QtyFalse, impulse is the change in velocity x the mass
Why do you want to land on a softer surface after a fall?When a surface "gives" there is a longer collision time ; the AVE F(net) is smaller
Why do cars have air bags?the airbag allows for a longer collision time during an impact
What are the two ways to change an objects momentummass - velocity
Change in Ug equationΔUg=Ug(f)-Ug(i)
PGE is alao calledUg
Change in Momentum EquationΔp=p(f)-p(i)
Magnitude of Δp is equal toIΔpI
T or F, a skateboarder needs a 0 F(net) between themselves and the board to balance on a skateboardTrue, if either the person or the board have a larger F(net) the person will fall.
Is a person on a skateboard a closed system? does the conservation of momentum change if you DO NOT fall?Yes - No
If a QTY in a closed system does not change after going through a series of changes we say that there is a _ of that QTYConservation
Conservation of Linear momentum - defineThe sum total of ALL linear momentum forces acting in a CLOSED system.
Use conservation of momentum to explain how a propeller driven plane flies through the airthe propellers have a momentum which causes the air to flow BACKWARDS. This momentum is countered by the FORWARD momentum of the plane.
how does a balloon fly through a vacuum - does this process need air?the escaping gasses have a momentum that propels them BACKWARD which propel the balloon FORWARD. - NO AIR IS NEEDED IN THE SPACE
If an equation does not EXPLICITLY have time _ is conservedEnergy
If an equation does not EXPLICITLY depend on a translation in space, _ is conservedLinear Momentum
If an equation does not EXPLICITLY depend on rotations of space, _ is conservedAngular Momentum
Impulse is in the _ direction as the _. this is also the same direction as the _same - Force - momentum
A _ is required to change the momentum of an objectForce
Change of an objects momentum equationΣF = Δp/Δt
Impulse-momentum theorem - equationThe change in the momentum of an object is equal to impulse of the F(net) acting on the particle - Δp=I (impulse is being applied by a Force)
Elastic Collision - DefineTotal kinetic energy before the collision is = to the kinetic energy AFTER the collision; total kinetic energy is conserved
Inelastic collisions - defineThe kinetic energy is NOT conserved; energy before does NOT equal after collision. Some energy is lost as THERMAL energy
Kinetic Energy equationKE=(1/2)(m)(v)^2
Most common type of energy is_ energyKinetic
The KE of an object increases with the _^2Speed
If an object DOUBLES it speed, the KE is _ times as large4 times as big
The KE of an object is _ proportional to its massDirectly
Unit for ALL energy is_. SI unit is _(Kg)(m^2/s^2) - joule (J)
T or F. KE is a vector QtyFalse, the KE is NOT dependent on the direction of motion
Elastic Collision - DefineThe initial KE is = to the Final KE
Inelastic Collision - DefineKE before collision is NOT = to KE after collision
Perfect inelastic collision - DefineExtreme inelastic collision in which the colliding objects stick together after the collision.
Outcome of collisions are determined by the _ of _ AND the extent to which KE is _Conservation of momentum - Conserved
If you drop a rubber ball on a hard surface and it returns to its ORIGINAL height, the collision is _elastic, because the KE is the same before and after the collision. (would never happen)
Conservation of energy - defineEnergy is never created or destroyed, it just changes states (heat, potential, KE, etc)
A _ is needed to for a change in KEF(net)
Work equation - unitsF=(force)(distance) - J (Also N*m, which is the same thing)
In order for work to be done there MUST be _Motion
Work is ALSO defined by _ (involves KE)ΔKE
F(net) and velocity in SAME direction = what kind of work?Positive work
F(net) and velocity in OPPOSITE direction = _ kind of workNegative work
T or F, momentum is a forceFalse, momentum is a Qty of motion
A car slowing down is an example of _ work - explainNegative work - the brakes apply a force that is OPPOSITE to the rotation of the wheels and is therefor negative, but because this force is applied WITHIN the same object its force is small. The roads friction force with the wheels is what does most of the slowing
A car traveling at 25 mph has only _ the KE as one traveling at 50 mph.1/4
For work to happen the forces have to be along the _ of _Direction of motion
Forces that are perpendicular to the motion of and object do _ workNo
In a constant circular motion there is _ work being done - explainnone because the forces are perpendicular to the motion
T or F. As a ball goes up vertically it INCREASES in KEFalse, the ball would be gaining PE
Gravitational Potential Energy (GPE) - Define - also shown asThe work that WOULD be done by gravity if an object fell from a particular point in space to the location assigned a value of 0 - Ug
GPE equation - unitsGPE=(mass)(accel of gravity)(height) - J
T or F. GPE increases as KE decreasesTrue
The GPE of an object at height X is = to ?the acceleration of gravity of the same object dropped the SAME distance ABOVE height X
T or F. moving an object horizontally changes the GPEFalse
Mechanical Energy - define - equationThe sum of KE and ANY types of potential energy. - ME=KE+(all types of) PE
T or F. When friction force can be ignored and only GPE is doing work, the ME of a system does NOT change - exampleTrue - free fall
In a swinging pendulum, the MAX GPE is at _ and the MAX KE is at _top of swing - middle of swing
A spring is an example of what kind of PE?Elastic PE
Chemical energy is PE associated with what phenomena Electro-magnetism
When friction forces interact with KE, what is created?Thermal energy
Power - define - equation - unitsThe change of energy from one type to another with respect to time - P = ΔE/Δt - W or (J/s)
Power measurement for MEHorse power
1 Horse power = _ watts746
KE is transformed into other forms of E during _ collisionsInelastic
KE is = to what amount of W done on the objectSame amount
T or F. KE can change into friction E - explainFalse - if friction is involved, the energy is transferred into Thermal energy. There is no such thing as Friction energy.
Work-energy Theorem - equationThe work done on an object is equal to the change in its KE - ΔK=K(f)-K(i)
Elastic Potential energy also called _U(s)
1 watt = _ J/s1 J/s