Physics 1010 exam 1

The brakes of a 1500−kg car exert a force of 3 kN. How long will it take for them to slow the car to a stop from an initial speed of 29 m/s?

*1 kN = 1000 N

density of water

1 gram/cm^3

1 joule =

1 kg m2 / s2

Unit conversions

1 mile = 1.61 kilometers 1 gallon = 3.79 liters 1 pound = 2.2 kilograms 1 Km = 1000 m 100 cm = 1 m 1 in. = 2.54 cm 1 m = 3.28 ft

Kinetic theory

1. Gas molecules are small and far apart 2. Gas molecules undergo elastic collisions 3. Gas molecules are non-interacting

The energy problem

1. Increasing demand for energy 2. Decline in supply of fossil fuels (81% of worlds energy) 3. Environmental concerns - CO2

velocity

d/t+ direction

density of water x volume displaced =

density of object x volume of object

Mass

density x volume

Friction

direction of this force always opposes the motion

Kinetic energy

directly proportional to the mass of the object and to the square of its velocity. KE = 1/2mv^2

velocity =

distance / time

phase changes

during a phase change energy is either consumed or released. Increasing energy from solid to liquid to gas to plasma

second law of thermodynamics

entropy cannot decrease (entropy = a measure of disorder)

Change in velocity

final velocity - initial velocity - can change by speeding up or slowing dow, or changing direction

action reaction theorem

forces occur in pairs

Air resistance during free fall

friction during free fall means net force is reduced, objects gain speed as they fall Resistance increases with speed, friction force becomes equal to gravity

Work =

fxd

Vector quantity

have direction and magnitude (size). ex. velocity

Heat flows from

higher temperature to lower temperature

accuracy

how close the measure is to the true value

Newton's third law

if one object exerts a force on a second one, then the second object exerts an equal but opposite reaction force

When the kinetic energy of an object is doubled (mass remaining constant), the momentum...

increases by about 40% (by 2, or 1.41 times). KE will be 2KE, and since mass can't be changed, the velocity must change.

centripetal force

inwards - what makes circular motion possible - proportional to the square of the velocity of the object and inversely proportional to the radius of a curved path Fc = mv^2/r Unit: N

Mass SI unit

kg

Energy unit

kilowatt/hr

volume

lwh, m^3

Velocity/speed

m/s - meters per second

force

mass x acceleration (ma) - measured in newtons (N) = kgm/s^2 1 kN = 1000 N

density (P = rho)

mass/volume, kg/m^2. this is an intrinsic property of an object that stays the same

power

measure of the rate at which work is accomplished work(or energy)/time (j/s)

Einstein's theory of relativity

measurements are relative and depend on which frame of reference you're using

work done against gravity

mgh

Buoyancy

net upwards pressure on any object immersed in a liquid

Inertial reference frame

no acceleration in this frame

Elastic collision

objects are not deformed after. Ex. Bouncy ball. energy is conserved.

scalar quantity

only contains info about magnitude. familiar scalar quantities include Temperature, power, mass

centrifugal

outwards

Ellipse

ovular shaped - the sum of the distances from 2 foci is constant for planets, the sun is at one foci

Linear momentum (denoted by P) equation

p = m x v.

Charle's law + Boyle's law --> Ideal gas law

pV/t = constant

Energy equation

power x time

Temperature

proportional to average kinetic energy of molecules that make up a substance

Energy=

pt

speed

rate of change of a position - does not contain directional information (scalar quantity)

Variable sources of energy

rate of energy production varies with the time of day ex. solar, tidal, wind, waves

precision

repeatability of the measurement using the same instrument

Same temperature =

same thermal energy

time unit

seconds

Motion of the earth around the sun

slower when farther away, faster when closer

Thermal expansion

solids expand as particles vibrate faster at higher temperatures

Heat

sum of the kinetic energy of all of the particles that make up a body

Retrograde motion

the apparent motion of a planet in a direction opposite to that of other bodies within its system, as observed from a particular vantage point.

most important convective heating

the atmosphere

Radiation

the emission of energy as electromagnetic waves or as moving subatomic particles, especially high-energy particles that cause ionization.

velocity of a falling object is directly proportional to

the length of time the object has been falling

Convection

the movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat. - fluids

conduction

the process by which heat or electricity is directly transmitted through a substance when there is a difference of temperature or of electrical potential between adjoining regions, without movement of the material. - Solids, molecular heat

Kepler's 3rd law

the ratio between the square of the time needed by a planet to make a revolution around the sun and the cube of its average distance from the sun is the same for all the planets. Te2/Re3 = Ta2/Ra3 Where Te = distance of earth from the sun (1AU) and Re=The distance of the earth from the sun

net force

the sum of all forces acting on an object

Source of all energy on earth

the sun

most important radiative head transfer

the sun! All objects radiate and absorb energy at all times. If there is more energy absorbed than given off, temperature goes up - pupils and dark surfaces

Heat engines

turns heat into mechanical energy by bringing a working substance from a higher state temperature to a lower state temperature.

Direction of the acceleration of swing of a pendulum at the midpoint?

upwards

Distance

v x t (speed x time) - meters (m)

Time =

v/g

Momentum can be 0 only if..

velocity is 0

acceleration due to gravity is always...

vertically downwards

power is measured in

watts

Buoyant force

weight of fluid displaced by a body - does not depend on the weight of the object - only on the weight of the displaced fluid = mass of displaced water x gravity = density of water x volume displaced x gravity weight = mg

terminal velocity

when air resistance equals gravitational force and they cancel out - net force = 0

insulator

wood, cork, air, snow

vertical velocity

√2gh

height

1/2gt^2

gravitational potential energy

1/mgh

Two tugboats are towing a ship. Each exerts a horizontal force of 3 tons and the angle between their towropes is 90°. What net force is exerted on the ship?

4.2. Pythagorean theorem

Big G Constant - Gravitational constant

6.67 x 10^-11 N

How many square feet are there in an area of 7.8 square meters?

84.2 ft^2 - 1 m = 3.28 ft. 1m^2 = 3.28^2 = 10.8 ft. 7.8 x 10.8 = 84.2

little g

9.8 m/s^2, this is a constant - every second, velocity is changing by 9.8

Kepler's 2nd law

A radius vector joining any planet to the Sun sweeps out equal areas in equal lengths of time

vector quantities are often represented by...

A straight line with an arrowhead The length of the line yields information about MAGNITUDE The arrow indicates the DIRECTION

Newton's law of gravitational force

ALL objects attract each other with a force of gravitational attraction. This force of gravitational attraction is directly dependent upon the masses of both objects and inversely proportional to the square of the distance that separates their centers. - Force of gravity is proportional to mass 1 + mass 2 / distance between centers

If the polar ice caps melt, the length of the day will increase. Why?

According to the Law of Conservation of Angular Momentum, if the level of the sea rises, the earth's spin on its axis will slow down.

Fossil fuels

All carbon based - petroleum products, coal, natural gas - rich in chemical potential energy - nonrenewable

Pressure facts

At a given depth, throughout a static connected fluid, pressure stays the same. Pressure increases the deeper you go

charles law

At constant pressure, and far from liquefaction, all gases have the same expansion coefficient. AKA volume of gas changes if temperature does - warm air expands - convection

Direction of acceleration in pendulum swing halfway down from the furthest point towards the midpoint?

At some angle to the path, pointing above the path

An object at rest can have.. A. Non-zero KE b. non zero gpe c. non zero momentum d. non zero velocity

B. Non-zero GPE. At rest object has no velocity. No velocity means no anything associated with velocity

Carbon capture and storage

CO2 emissions from coal burning facilities are captured and pumped via pipeline deep into the earth

Kepler's 1st law

Elliptical foci - planetary orbits are ellipses with the Sun at one focus of the ellipse

Universal law of gravity

F = m1 x m2 / distance^2 x G

Law of conservation of momentum

For a collision occurring between object 1 and object 2 in an isolated system, the total momentum of the two objects before the collision is equal to the total momentum of the two objects after the collision. Momentum can be exchanged.

When falling...

GPE decreases. Kinetic energy increases. Together there is no change. The change occurs when the object hits the ground.

Ptolemy

Geocentric model

How does a nuclear power plant produce electricity?

Heat from nuclear fissions in the reactor produces steam that drives turbines connected to electric generators.

Copernicus

Heliocentric model

Energy is measured in

Joules

Momentum is greatest where..

Kinetic energy is greatest because this is where velocity is the greatest

The north star - polaris

Looks stationary relative to other stars for observers on Earth since it is aligned with the Earth's axis of rotation

Best thermal conductors

Lots of electrons - gold, silver, copper

Where is KE greatest on a pendulum?

Lowest point the bottom (max at lowest point, min at highest)

Angular momentum

Momentum associated with the rotation of a body about some axis. The direction of this momentum is parallel to the axis of rotation

Right now, you are sitting perfectly still in your seat what is the NET FORCE being exerted on your body?

NET force = 0 The force down from gravity and the force up from the chair cancel out!

What must be your location if the stars move across the sky in circles centered directly overhead?

North or South Poles

Pressure

Pascals - 1 kP = 1000 p. Pressure = force over constant area a = f/a. Smaller area? More pressure

The diagram shows a planet orbiting the sun. Where is the planet's angular momentum the greatest?

Same everywhere - Angular momentum is conserved because there is no external torque on the system

The acceleration of gravity on the surface of Venus is 8.9 m/s2. What would happen to a ball thrown upward on Venus compared to one thrown upward with the same speed on Earth? (Atmospheric resistance is neglected).

T = total time of flight = 22h / g. Since g is smaller on Venus than Earth, T will be greater and the ball will return to the ground later on Venus.

Newton's second law

The acceleration of any object is directly proportional to the net force on the object and inversely proportional to its mass. a=f/m

If the moon were half as far from the earth as it is today, how would the gravitational force it exerts on the earth compare with the force it exerts today?

The force would be four times what it is today.

The earth takes almost exactly 24 h to make a complete turn on its axis, so we might expect each high tide to occur 12 h after the one before. However, the actual time between high tides is 12 h 25 min. What can account for this?

The moon is moving relative to the earth, changing the times of high and low tides by 50 minutes in 24 hours.

In terms of what you would actually observe, what does it mean to say that the moon apparently moves eastward among the stars?

The moon's position will move eastward of any reference star when observed on consecutive nights.

Special relativity

The moving object at constant velocity with no acceleration - inertial reference frame

First postulate of theory of relativity

The speed of light is constant

Kepler's third law

The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.

A year corresponds to the time it takes for an observer on the earth to see.....

The sun migrate eastward completely around the sky

Inelastic collision

There is deformation after the collision. Energy is not conserved - it dissipates into other forms

If the Earth had no Moon then what would happen to the tides?

There would be small but noticeable tides and they would occur less often

Newton's first law

When no net force is acting on an object, an object at rest will remain at rest and an object in motion will remain in motion

Nuclear fission

Where nuclear energy comes from - the breaking apart or decomposition of large nuclei - usually uranium

The length of day has varied. When did the longest day thus far occur?

Yesterday, because the day's length has been increasing steadily for 380 million years

rate

a change in any quantity proportional to time

motion

a change in position

why do we have two high tides in a day?

a. the earth moon gravitational force b. the earth is not spinning on its central axis. water is pushed outwards as it rotates due to centrifugal force`

Change in speed is calculated by

acceleration x time. final speed = initial speed + change in speed

Acceleration to gravity only...

acts in the VERTICAL direction

calorie

amount of energy needed to raise the temperature of one kg of water by 1ºC

Specific heat

amount of heat needed to raise the temperature of 1 kg of water by 1º celsius: Q=mc∆t

Archimedes principle

an immersed body experiences an upward force equal to the weight of the fluid displaced by the body.

Boyle's law

at constant temperature, pressure x volume is constant. P1/p2 = v2/v1 - compressed gas has higher pressure

constant acceleration

can calculate this if we know final and initial velocity and acceleration.

Continuous energy source

can supply energy continuously ex. hydroelectric, geothermal

converting celsius to Fahrenheit

celsius x (9/5) + 32

acceleration

change in velocity/time. Occurs when there is a change in speed or direction. Common units: m/s^2, ft/s^2, mph^2

Gasification

coal transformed into a mixture of gases - syngas - can be used in methane production (which is cheap and renewable)

You are driving your car and approaching a stop sign. You apply the brakes when your speedometer reads 27 m/s (60 mph). If you know that the breaks will provide an acceleration of a = - 6m/s2, how far away must you apply the brakes?

d = v1t + 1/2at^2