Phys 124

Which statement describes photons most accurately?

a. Photons have no mass but do have momentum b. Photons have mass but no momentum c. Photons have a birthday sometime in September

but because of quantum mechanics

The importance of the Compton effect is to show that Select one: a. photons have wave-like properties b. electrons have wave-like properties c. atoms have particle-like properties d. atoms have wave-like properties e. photons have particle-like properties

E

Quantum tunnelling refers to: Select one: a. a particle appearing on the other side of a region where the particle cannot exist

according to the laws on classical mechanics. b. the passage of photons through the tip of a scanning tunnelling microscope c. a particle using its wave-like properties to build an intricate underground network of passages d. protons passing through a thin sheet of gold foil and bouncing off the heavy nuclei. e. a wave propagating through a piece of glass and experiencing total internal reflection.

If the wavelength of light used to make a two slit interference pattern is doubled

how will the interference patten change? Select one: a. The spacing of the bright fringes will increase b. The spacing of the bright fringes will decrease c. The brightness of the bright fringes will decrease d. The brightness of the bright fringes will increase.

You can determine the work function for a metal by Select one: a. shining higher and higher frequency photons on the metal until electrons are emitted b. Measuring the mass of the metal and the distance through which it is moved c. heating the metal and looking for the peak emission according to Wien's Law d. Increasing the intensity of the light on the metal until electrons are absorbed e. measuring kinetic energy of electrons emitted below the cutoff frequency.

A

Planck's theoretical explanation for blackbody radiation relied upon Select one: a. Defining the Wien displacement law on a quantized grid of wavelengths b. Selecting a value for the speed of light that was a quantized multiple of the frequency c. Defining a blackbody to be an ideal body that absorbs all radiation d. Assuming the energy in a blackbody came only at specific values e. Letting light waves take on every possible value of energy

D

Consider two objects that are originally separated by a distance d and feel a gravitational force between them. How would the distance between them change if the force that is felt is quadrupled (increased by a factor of 4)?

Select one: a. Decrease distance by a factor of 2 b. Increase distance by a factor of 2 c. Decrease distance by a factor of 4 d. Increase distance by a factor of 4

A

The Earth exerts a gravitational force of magnitude F on the Moon. Imagine the Earth has 100 times more mass than the Moon. What is the magnitude of the gravitational force that the Moon exerts on the Earth?

Choose the closest answer. Select one: a. 10F b. F c. 3.2F d. 100F

B

If g = 9.81 m/s2 is the acceleration of gravity at the Earth's surface. astronauts in the International Space Station feel an acceleration due to gravity from the Earth that is most nearly:

Select one: a. 0.1g b. 0 c. 0.9g d. 1.0g e. 0.25g

C

The Earth and the Sun are 1x108 km apart. The magnitude of their gravitational potential energy is some quantity U. Jupiter and the Sun are 1x109 km apart. Jupiter is 100 times the mass of the Earth. What is the magnitude of the gravitational potential energy between Jupiter and the Sun?

Select one: a. 1 U b. 10 U c. 0.01 U d. 100 U

B

The motion of a particle in a longitudinal wave can be described as

Select one: a. left and right

perpendicular to the direction of wave propagation b. up and down

To double the speed of a wave on a string

you would have to

Select one: a. double the mass-per-length of the string b. decrease the mass-per-length by a factor of twot c. increase the tension in the string by a factor of 4. d. reduce the tension in the string by a factor of 4. e. reduce the tension in the string by a factor of 2.

Two sound waves with the same frequency

phase

Which of the following materials would have the highest speed of sound?

Select one: a. Helium at 0 °C b. Air at 20° C c. Steel d. Water at 0° C

C

Consider a situation where you are standing on the straight line between two audio speakers but do not hear anything because of wave interference. What is the shortest distance (in wavelengths of sound λ) that you would have to move toward one speaker to hear the sound at its loudest?

Select one: a. λ/2 b. λ/4 c. λ d. 3λ/4

B

What is the approximate frequency of your heartbeat? Select one:

a. 1 Hz b. 0.03 Hz c. 37.3 kHz d. 0.1 mHz e. 1 kHz

A

If an object is in simple harmonic motion about the position x=0

what is true about kinematic quantities of the object relating the position x to the velocity and acceleration?

Select one: a. When the position is positive

If the total energy in a spring oscillator is 15 J

what describes the balance of energy between kinetic (K) and spring potential energy (Us) when the mass is at the equilibrium position of the oscillator?

Select one: a. K= 7.5 J

A ball of mass m=335.9 g is thrown straight up into the air with an initial speed vi= 7.6 m/s. Find the magnitude of the momentum of the ball when it is halfway to its maximum height.

Select one: a. 2.55 kg m/s b. 1.28 kg m/s c. 1.11 kg m/s d. 0 kg m/s e. 1.81 kg m/s

What are the steps to solve?

hmax = vi^2/2g

Speed at the half of the max height: vf^2−vi^2 = −2g(1/2hmax) =−ghmax

vf^2 = −ghmax + v2i = (1/2vi^2)

pf = mvf =mvi/(√2)

ANSWER: E

A hockey puck (m1=0.4 kg) is sliding along the ice in the +y direction with a speed of v1=5.2 m/s. It collides with curling rock m2=6.7 kg travelling in the +x direction with speed v2 = 0.18 m/s and the two objects stick together. At what angle with respect to the +x axis does the combined object travel after the collision?

Select one: a. 88.0° b. 30.1° c. 0.0° d. 59.9° e. 3.4°

Show steps to solve

Since the collision is perfectly inelastic: px

Swimmers at a water park have a choice of two frictionless water slides

as shown in the figure below. Although both slides drop over the same height h

Consider two springs (A and B) with spring constants kA = k and kB = 2k that are used to launch two separate balls. Spring A launches a ball with mass m and Spring B launches a ball that has a mass 2m. During the launch

spring A is compressed by a distance 2D and spring B is compressed by a distance D. How does the work done by Spring A on its ball (WA) compare to the work done by Spring B on its ball (WB)?

a. WA = 0.5 WB b. WA = WB c. WA = 0.25 WB d. WA = 4 WB e. WA = 2 WB

Explain choice

An egg falls from a bird's nest in a tree and friction effects due to air resistance is negligible. As it falls

a. Both its kinetic energy and its momentum are conserved. b. Only its mechanical energy is conserved. c. Only its momentum is conserved. d. Only its kinetic energy is conserved. e. Both its mechanical energy and its momentum are conserved.

Explain choice

A car (mass m

speed 3v) and a truck (mass 3m

A rigid body is rotating with a constant period of rotation. Which of the following statements is correct?

a. All points on the body have different angular velocities and different tangential velocities. b. All points on the body have the same angular velocity but different tangential velocities. c. All points on the body have different angular velocities and the same tangential velocity. d. On all points on the body

the angular velocities and tangential velocities are equal and opposite. e. All points on the body have the same angular velocity and the same tangential velocity.

Two spinning disk (disk 1 and disk 2) are rolling without slipping. The mass of disk 1 is four times the mass of disk 2. The radius of disk 2 is double the radius of disk 1. The translational speed of disk 1 is equal to that of disk 2. If we denote the angular velocities of each disk as ω1 and ω2 and their rotational kinetic energies as Kr1 and Kr2

which of the following statements is correct:

a. ω1 = 4ω2

R1 = R

R2 = 2R

How much work is done by a constant force F~ = −Fxx + Fyy N acting through a displacement ~d = dxxˆ + dyyˆ m

Solution: W = −Fxdx + Fydy

A clown of mass mc kg is shot from a cannon with horizontal speed of v m/s and lands (and sticks) on a disk-shape rotating merry-go-round of mass M kg and radius R m. The landing spot (star) is at the halfway point between the centre and the outer edge as shown in the image below. If the merry-go-round is at rest before the clown lands

and if air resistance while the clown is in flight is negligible

A heavy rock and a light rock are dropped from the same height and experience no air resistance as they fall. Which of the following statements about these rocks is correct?

a) The work done by gravity on each rock is equal. b) The heavier rock reaches the ground before the lighter rock c) Just as they were released

both rocks had the same amount of gravitational potential energy. d) Both rocks have the same kinetic energy when they reach the ground e) Both rocks have the same speed when they reach the ground

Using dimensional analysis

what does v2/x equal?

a) t (time) b) a (acceleration) c) v (speed or velocity) d) x (position or distance) e) m (mass

Peta = ????

10^15

Tera = ???

10^12

Giga

10^9

Mega

10^6

kilo

10^3

centi

10^-2

milli

10^-3

micro

10^-6

nano

10^-9

pico

10^-12

femto

10^-15

Pm = ???

10^15 m

Tm = ???

10^12 m

Gm = ???

10^9 m

Mm = ???

10^6 m

km = ???

1000 m or 10^3 m

cm = ???

10^-2 m

mm = ??

10^-3 m

um = ???

10^-6 m

nm = ??

10^-9 m

pm = ??

10^-12 m

fm = ??

10^-15 m

How many nanometres is 0.2 km?

A. 2×106^-13 nm B. 2×10^8 nm C. 2×10^9 nm D. 2×10^11 nm E. 2×10^13 nm

D

displacement

How far something is from where it started.

Distance

How far something has travelled in its motion. (= total length of travel)

Decreasing

positive velocity

Increasing position

T/F: acceleration is always down even if initial velocity is up!

TRUE

You throw a ball straight up into the air. After it leaves your hand

at what point in its flight does it have the maximum value of acceleration?

a) Its acceleration is constant everywhere. b) At the top of its trajectory c) Halfway to the top of its trajectory d) Just after it leaves your hand e) Just before it returns to your hand on the way down

Scalar

: a numerical value. May be positive or negative. Examples: temperature

Vector:

a quantity with both magnitude and direction. Examples: displacement (e.g.

PROJECTILE MOTION EQUATION

a = 0x -gy

A small cart is rolling at constant velocity on a flat track. It fires a ball straight up into the air as it moves. After it is fired

what happens to the ball?

a) It depends on how fast the cart is moving. b) It falls behind the cart. c) It falls in front of the cart. d) It falls right back into the cart. e) It remains at rest.

Now the cart is being pulled along a horizontal track by an external force (a weight hanging over the table edge) and accelerating. It fires a ball straight out of the cannon as it moves. After it is fired

what happens to the ball?

a) It depends upon how much the track is tilted. b) It falls behind the cart. c) It falls in front of the cart. d) It falls right back into the cart. e) It remains at rest

A person standing at the edge of a cliff throws one ball straight up and another ball straight down at the same initial speed. Neglecting air resistance

the ball to hit the ground below the cliff with the greater speed is the ball initially thrown:

A. upward B. downward C. neither — they both hit at the same speed. D. Need more info

How does the angle of trajectory affect the time in air?

Higher angle = longer time

___________________vector is always tangent to the trajectory

VELOCITY

What is the equation for air time at a launch angle of zero ?

√(2h/g)

Equation for Range

(v0^2/g)sin2θ

When is Rmax achieved?

θ = 45

Rmax =

(v0^2)/g

t-hang =

(2v0sinθ)/g

h-max =

(v₀sinθ)²/2g

h-max in terms of g =

(g/8) (t-hang)²

As the temperature of a black body increases what happens to the peak wavelength of the radiation?

a) It increases b) It decreases c) It remains constant d) It depends on the temperature

B

as the temperature increases the peak frequency increases. The Wavelength is proportional to the inverse of the frequency so it will decrease

Wien's Displacement Law Equation

fpeak = (5.88 x 10^10s^-1 ∙ K^-1)T

Which has more energy

a photon of:

a) red light b) yellow light c) green light d) blue light e) all have the same energy

What is the cutoff wavelength?

the maximum wavelength to knock out electrons

higher wavelengths are not knocked out

A metal surface is struck with light of ƛ = 400 nm

releasing a stream of electrons. If the light intensity is increased (without changing ƛ)

Photons have no rest ________ but they carry ______________

Photons have no rest mass but they carry momentum

If the wavelength of a beam of light is decreased

what happens to the momentum of the photons?

a) It increases. b) It decreases. c) It stays the same. d) It depends on the wavelength

in terms of wavelength of light

what is the momentum equation?

What is the Compton effect?

when an incoming electron ejects the orbital electron and transferring part of the energy which creates a new

a ripple occurs

In the compton effect

when does max change occur?

DeBroglie Hypothesis states that

Particles have properties of waves as well as properties of particles

proton with the __________velocity will have the longer wavelength.

proton with the smaller velocity will have the longer wavelength.

ƛ = h/mv

if the particles have the same momentum

they will also have _______________ wavelength

Electrons have short wavelengths compared to light and can interfere through narrow slits (______ scale). This is comparable to separation between atoms

nm scale

Heisenberg Uncertainty Principle (3)

states that it is impossible to determine simultaneously both the position and velocity of an electron or any other particle

uncertainty in position ↔ uncertainty in wavelength

Energy of a body cannot be determined with 100% accuracy at exactly known time moment

Quantum tunnelling effect

possibility for a particle to pass through a classically forbidden region and emerge on the other side of the potential barrier.

Tunnelling occurs because of the wave description of ___________. The barrier acts like a mass on a ___________.

Tunnelling occurs because of the wave description of particles. The barrier acts like a mass on a string.

If the barrier is infinitely high in quantum tunnelling

(corresponding to end of string is fixed)

But if the height is finite (non-fixed end)

some wave will __________and some will _____________

This is because a wave is a continuous ____________. It cannot have ____________changes in its properties unless there is a huge _________________

If the width of the "classically forbidden region" is smaller or of the same order as the wavelength

tunnelling is ______________