Physics Midterm 3

If the entire volume expands, it is called

volume thermal expansion. It can occur for solids, liquids and gases.

he separation between the ice and steam points on the Celsius scale is divided into

100 C degrees

while on the Fahrenheit scale the separation is divided into

180 F degrees

Therefore, the size of each Celsius degree is larger than that of each Fahrenheit degree by a factor of

180/100, or 9/5 In other words, each degree in Celsius scale has 9/5degrees of Fahrenheits. T(°F) = 𝟗/𝟓 T(°C) + 32

However, the ice point 0°C occurs at

273.15 K on the Kelvin scale. Thus, the Kelvin temperatureT(K) and the Celsius temperature T(°C) are related by T(K) = T(°C) + 273.15 The number 273.15 is an experimental result, obtained in studies that utilize a gas-based thermometer.

If the ball is thrown upwards, the work done by gravity is A. Positive B. Negative C. Zero

B. Negative

A mass attached to a vertical spring causes the spring to stretch and the mass to move downwards. What can you say about the spring's potential energy (PESPRING) and the gravitational potential energy(PEGRAVITY) of the mass A. both PESPRING and PEGRAVITY decrease B. PESPRING increases and PEGRAVITY decreases C. both PESPRING and PEGRAVITY increase D. PESPRING decreases and PEGRAVITY increasesE. PESPRING increases and PEGRAVITY is constant

B. PESPRING increases and PEGRAVITY decreases

A 92.0-kg skydiver with an open parachute falls straight downwardt hrough a vertical height of 325 m. The skydiver's velocity remains constant. What is the work done by the non-conservative force of air resistance, which is the only non-conservative force acting? A. -2.93 × 10 5 J B. 0 J C. 2.93 × 10 5 J D. The answer is not obtainable, because insufficient information about the skydiver's speed is given.QUESTION

A. -2.93 × 10 5 J

What is the work done by a force of 10 N if the displacement is 10 m and is perpendicular to the force? A. O J B. 1 J C. 10 J D. 100 J

A. O J

What is the work done by gravity on the ball if it is thrown at an upward angle as demonstrated by the ball on the right? A. mg(hf - h 0) B. > mg(hf - h 0) C. < mg(hf - h 0)

A. mg(hf - h 0) The work depends only on the initial and final values of the height and does not depend on the exact path in which the ball falls to the ground!!

Robert pushes the box to the left at constant speed. In doing so, Robert does ______ work on the box. A. positive B. negative C. zero

A. positive

A suitcase is hanging straight down from your hand as you ride an escalator. Your hand exerts a force on the suitcase, and this force does work. This work is A. positive when you ride up and negative when you ride down B. negative when you ride up and positive when you ride down C. positive when you ride up or down D. negative when you ride up or down

A. positive when you ride up and negative when you ride down

A crane lowers a girder into place at constant speed. Consider the work W G done by gravity and the work W T done by the tension in the cable. Which is true? A. W G > 0 and W T > 0 B. W G > 0 and W T < 0 C. W G < 0 and W T > 0 D. W G < 0 and W T < 0 E. W G = 0 and W T = 0

B. W G > 0 and W T < 0

Robert pushes the box to the left at constant speed. While doing so, the work done on the box by force of friction is A. Always zero. B. Always positive. C. Always negative.

C. Always negative.

However, the Moon revolves around the Earth along an elliptical path. Along any part of the orbit the Earth does A. Positive work on the Moon B. Negative work on the Moon C. Could be either A or B D. No work on the Moon

C. Could be either A or B

If the Moon revolves around the Earth in a circular path of fixed radius with constant speed, along any part of the orbit the Earth does A. Positive work on the Moon B. Negative work on the Moon C. No work on the Moon

C. No work on the Moon

Starting from rest, a marble first rolls down a steeper hill, then down a less steep hill of the same height. For which is it going faster at the bottom?Assume no friction or air resistance. A. Faster at the bottom of the steeper hill. B. Faster at the bottom of the less steep hill. C. Same speed at the bottom of both hills. D. Can't say without knowing the mass of the marble.

C. Same speed at the bottom of both hills. HEIGHT IS THE SAME

A person is riding on a Ferris wheel. When the wheel makes one complete turn, the net work done on the person by the gravitational force ________. A. is positive B. is negative C. is zero D. depends on how fast the wheel moves E. depends on the diameter of the wheel

C. is zero ended up in the same spot

A spring-loaded gun shoots a plastic ball with a launch speed of 2.0 m/s. If the spring is compressed twice as far, the ball's launch speed will be A. 1.0 m/s B. 2.0 m/s C. 2.8 m/s D. 4.0 m/s E. 16.0 m/s

D. 4.0 m/s

The work W0 accelerates a car from 0 to 50 km/hr. How much work is needed to accelerate the car from 50 km/hr to 150 km/hr? A. 2 W0 B. 3 W0 C. 6 W0 D. 8 W0 E. 9 W0

D. 8 W0

Two forces F 1 and F 2 act on a particle. As a result the speed of the particle increases. Which one of the following is NOT possible? A. The work done by F 1 is positive, and the work done by F 2 is zero. B. The work done by F 1 is zero, and the work done by F 2 is positive. C. The work done by each force is positive. D. The work done by each force is negative. E. The work done by F 1 is positive, and the work done by F 2 isnegative.

D. The work done by each force is negative.

By what factor does the kinetic energy of a car change when its speed is tripled? A. no change at all B. factor of 3 C. factor of 6 D. factor of 9 E. factor of 12

D. factor of 9

A box is being moved with a velocity 𝒗 by a push force 𝑭𝑷 (in the same directionas 𝒗) along a level horizontal floor. The normal force is 𝑭𝑵 , the kinetic frictionalforce is 𝑭𝒇 𝒌 , and the weight is 𝑭𝑮 = 𝒎𝒈. Which one of the following statementsis correct? A. 𝑭 𝑷 does positive work, 𝑭 𝑵 and 𝑭 𝒇 𝒌 do zero work, and 𝑭 𝑮 does negative work. B. 𝑭 𝑵 does positive work, 𝑭 𝑷 and 𝑭 𝒇 𝒌 do zero work, and 𝑭 𝑮 does negative work. C. 𝑭 𝒇 𝒌 does positive work, 𝑭 𝑵 and 𝑭 𝑮 do zero work, and 𝑭 𝑷 does negative work. D. 𝑭 𝑷 does positive work, 𝑭 𝑵 and 𝑭 𝑮 do zero work, and 𝑭 𝒇 𝒌 does negative work.

D. 𝑭 𝑷 does positive work, 𝑭 𝑵 and 𝑭 𝑮 do zero work, and 𝑭 𝒇 𝒌 does negative work.

NON- CONSERVATIVE FORCE

DEPENDS ON THE PATH TAKEN BY THE OBJECT A force is non-conservative when the work it does on a moving object is dependent on the path between the object's initial and final positions. Eg 1: Work done by force of friction depends only on the length of the path covered. Eg 2: Force of tension Eg 3: Push or pull by a person Eg 4: Air resistance

CONSERVATIVE FORCE :

DOES NOT DEPEND ON THE PATH TAKEN BY THE OBJECT A force is conservative when the work it does on a moving object is independent of the path between the object's initial and final positions. Eg1: Work done by force of gravity depends only on the height from the ground and not on the path taken to reach that height. Eg2: Work done by spring/elastic force depends only how much the spring is compressed or stretched. Doesn't care if it is stretched or compressed.

A net external non-conservative force does positive work on a particle.Based solely on this information, you are justified in reaching only one of the following conclusions. Which one is it? A. The kinetic and potential energies of the particle both decrease. B. The kinetic and potential energies of the particle both increase. C. Neither the kinetic nor the potential energy of the particle changes. D. The total mechanical energy of the particle decreases. E. The total mechanical energy of the particle increases.

E. The total mechanical energy of the particle increases.

ABSOLUTE ZERO

Experiments have shown that there exists a lowest possible temperature, below which no substance can be cooled.This lowest temperature is defined to be the zero point on the Kelvin scale and is referred to as If the straight line is extended or extrapolated to lower and lower temperatures, the line crosses the temperature axis at -273.15 °C

Conservative force and potential energy

For every conservative force, we can define a corresponding potential energy. The gain in KE is at the cost of PE of the conservative system, and viceversa. Hence, 𝑪𝒉𝒂𝒏𝒈𝒆 𝒊𝒏 𝑲𝑬 = − 𝑪𝒉𝒂𝒏𝒈𝒆 𝒊𝒏 𝑷𝑬 = Work" ∆𝑲𝑬 = −∆𝑷𝑬 = 𝐖

There are one hundred divisions between the ice and steam points on both

Kelvin and Celsius scales

MECHANICAL ENERGY

Kinetic energy + potential energy is known as the mechanical energyof an object! 𝑇𝑜𝑡𝑎𝑙 𝑀𝑒𝑐ℎ𝑎𝑛𝑖𝑐𝑎𝑙 𝑒𝑛𝑒𝑟𝑔𝑦 = 𝐾𝐸 + 𝑃𝐸

POTENTIAL ENERGY (U or PE)

Potential energy is stored energy and is associated with an object's position. Eg 1: Gravitational Potential Energy (GPE) Eg 2: Elastic/Spring Potential Energy (EPE/SPE)

A healthy person has an oral temperature of 98.6 °F. What would this reading be on the Celsius scale?

Tc=5/9(Tf-32) = 37 degree celcius

𝜶L 0∆𝑻

Temperature must be in °C. Length and change in length must be in meters. α Coefficient of linear expansion (Unit : °C-1 ) It is a constant, and depends on the element that makes up the rod. Higher the value of α, faster will the object expand along its length when it is heated.Effect of heat on solid: Linear Thermal Expansion𝑰 𝒏𝒄𝒓𝒆𝒂𝒔𝒆 𝒊𝒏 𝒕𝒉𝒆 𝒍𝒆𝒏𝒈𝒕𝒉 𝒐𝒇 𝒕𝒉𝒆 𝒓𝒐𝒅= ∆𝑳= L - L 0= 𝜶L 0∆𝑻

Significance of Absolute Zero

Temperatures lower than -273.15 °C cannot be reached by continually cooling a gas or any other substance.If lower temperatures could be reached, then the object would have a negative absolute gas pressure, which has no meaning. Thus, the Kelvin scale is chosen so that its absolute zero temperature is the lowest temperature attainable.

Elastic/Spring Potential Energy (U or more specifically SPE/EPE)

The energy stored in a spring when it is stretched or compressed is known as its elastic/spring potential energy

Temperature is generally measured using either theFahrenheit or the Celsius scale.

The freezing point of water is 0°C, or 32°F; the boiling point of water is 100°C, or 212°F.

WORK DONE BY FORCE OF GRAVITY

The negative sign indicates that the work is done at the expense of the GPE. However, total energy of the system must be conserved. Hence, this GPE is converted into the KE of the object such that:GPE + KE = Total mechanical energy = constant In other words, increase in KE is exactly equal to the decrease inPE in the system, and that is the work done on the object ∆𝑲𝑬 = −∆𝑷𝑬 = 𝐖 The work depends only on the initial and final values of the height and does not depend on the exact path in which the ball falls to the ground!!

In reality, no gas can be cooled to this temperature, because all gases liquify before reaching it.• However, helium and hydrogen liquify at such low temperatures that they are often used in the thermometer.

The pressure P is the magnitude F of the force acting perpendicular to a surface divided by the area A over which the force acts => P = F/A It is a scalar quantity

GRAVITATIONAL POTENTIAL ENERGY (PE or more specifically GPE) 𝑮𝒓𝒂𝒗𝒊𝒕𝒂𝒕𝒊𝒐𝒏𝒂𝒍 𝒑𝒐𝒕𝒆𝒏𝒕𝒊𝒂𝒍 𝒆𝒏𝒆𝒓𝒈𝒚 (𝑮𝑷𝑬) = 𝒎𝒂𝒔𝒔 × 𝒈 × 𝒉𝒆𝒊𝒈𝒉𝒕 𝒇𝒓𝒐𝒎 𝒈𝒓𝒐𝒖𝒏𝒅 𝑮𝑷𝑬 = 𝒎𝒈∆𝒉

The roller coaster's gravitational potential energy depends on its height above the ground. The greater its height is from the ground, greater is its stored energy i.e. gravitational potential energy. The greater its mass, greater is its gravitational potential energy.

CONSERVATION OF ENERGY.CONSERVATION OF ENERGY

There is a law that governs all natural phenomena that are known to date. There is no known exception to this law—it is exact so far as we know. It states that there is a certain numerical quantity, which we call energy. It says that this numerical quantity does not change no matter what happens in this Universe

𝐊𝐄 + 𝐏𝐄 = 𝒄𝒐𝒏𝒔𝒕𝒂𝒏𝒕

This means, if KE increases, PE decreases by the same amount, and vice versa. But total mechanical energy ( i.e. KE+PE) never changes for an object under the influence of conservative force/s

WORK DONE BY A SPRING

W = - ∆𝑺𝑷𝑬 The negative sign indicates that the work is done at the expense of theSPE. However, total energy of the system must be conserved. Hence, this SPE is converted into the KE of the object such that:SPE + KE = Total mechanical energy = constant The work depends only on how much the spring is compressed or stretched, and does not care about which of those two actions are undertaken as long as the length of the spring changes by ∆𝑥

Work-kinetic energy theorem states that:

W = ∆𝑲𝑬 - always true for all kinds of forces

Most materials contract when

cooled

The work done by conservative forces, Wc

does not depend of the path along which the object moves only depends on the initial and final positions. does no net work on an object moving around a closed path, starting and finishing at the same point. Since ∆KE = - ∆𝑮𝑷𝑬 # ∆KE + ∆𝑮𝑷𝑬 = ∆E = 0 # E = Constant

For some forces, like gravitational force and spring/elastic force

he source of this force is a well-defined potential energy, and the change in this potential energy can be related to the change in KE and the work done. These forces are known as conservative forces. W C = ∆𝑲𝑬 = −∆𝑷𝑬 - true only for conservative forces like gravity and spring/elastic forces

Most materials expand when

heated

the system is not interacting with the environment

isolated system, the total energy of the system is unchanged

Since work does not convey directional information

it is a scalar quantity

If the expansion is in any one dimension of a solid (Eg: Only along the length), it is called

linear thermal expansion. It occurs only in solids

If the force has a component in the direction opposite to the displacement, then the work done by that force is

negative

Is the principle of conservation of mechanical energy obeyed if An object moves uphill with an increasing speed

no the object is moving uphill, increasing GPE, while KE is increasing

Is the principle of conservation of mechanical energy obeyed if An object moves downhill with a constant speed.

no. KE is constant so PE (GPE) should stay constant

and decreases when the net force does negative work

object slows down (𝒗𝟎 > 𝒗𝒇 )

The kinetic energy increases when the net force does positive work

object speeds up (𝒗𝟎 < 𝒗𝒇 )

If the force has a component in the direction of the displacement, then the work done by that force is

positive

Kinetic energy

the energy of ano bject due to its motion. All moving objects have kineticenergy. The more massive an object, the larger isi ts kinetic energy. The faster it moves, the larger is its kineticenergy.KINETIC ENERGY (KE)SI unit: joule (J) = 1 kg m2/s2 𝑲𝒊𝒏𝒆𝒕𝒊𝒄 𝑬𝒏𝒆𝒓𝒈𝒚 = 𝟏/𝟐 𝒎𝒂𝒔𝒔×𝒗𝒆𝒍𝒐𝒄𝒊𝒕𝒚

If the object does not move

the force acting on the object does no work!! Work done by a constant force:Force and displacement in the same direction

If the kinetic energy decreases, the gravitational potential energy increases.

yes

If the kinetic energy does not change, the gravitational potential energy also does not change

yes

Is the principle of conservation of mechanical energy obeyed if An object moves uphill with a decreasing speed

yes

If there is no component of force along the direction of displacement, work done by that force is

zero

Effect of heat on solid: Linear Thermal Expansion 𝑰𝒏𝒄𝒓𝒆𝒂𝒔𝒆 𝒊𝒏 𝒕𝒉𝒆 𝒍𝒆𝒏𝒈𝒕𝒉 𝒐𝒇 𝒕𝒉𝒆 𝒓𝒐𝒅=

∆𝑳= L - L 0= 𝜶L 0∆𝑻

Work done by a constant force

𝑊𝑜𝑟𝑘 = 𝑭. 𝒔= │𝐹𝑜𝑟𝑐𝑒││𝐷𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡│ cos 𝜃

WORK - KINETIC ENERGY THEOREM (combining the idea of work, force and energy)

𝑾= Fscos𝜽 = 𝟏/𝟐 𝒎𝒗𝒇𝟐 - 𝟏𝟐 𝒎𝒗𝟎𝟐 = ∆𝑲𝑬

ENERGY CAN BE TRANSFORMED FROM ONE FORM TO ANOTHER

𝒎𝒈 𝒉 𝒇 − 𝒉𝒊 = − 𝟏/𝟐 𝒎(𝒗𝒇𝟐 - 𝒗𝒊𝟐 )