Unit 14: Physics 2 Part B

Single-Lens System?

- All object distances are positive. - All images and focal points on the same side of the lens or mirror as the observer are positive. - All images and focal points on the opposite side of the lens or mirror as the observer are negative. - Negative, virtual images are always upright.

Block B weighs 2/5 less than Block A. If Block A is placed a distance x from a fulcrum, where should Block B be placed to balance the fulcrum?

2/5 Block B is less than Block A, which means that Block B weighs 3/5 more than Block A. If it is 3/5 more than Block A, then is it 5/3 away from the fulcrum.

For a simple circuit containing a battery, a resistor and a capacitor, which of the following changes will increase the strength of the electric field between the capacitor plates?

Decreasing the distance between the capacitor plates.

The dark bands corresponds to a point where 2 light waves differ in phase by?

180 degrees.

The ambient noise at a raucous college football game increases from 10 decibels to 30 decibels. What could have accounted for this increase?

30-10 = 20, so it is 100 = intensity or volume. - the amplitude increased by a factor of 10. - the volume increased by a factor of 100. - the intensity increased by a factor of 100.

If particle A has a negative charge of (x), and particle B has a positive charge of (x). X is the same number. What would increase the strength of the electric field?

All would increase: - Moving Particle A towards Particle B. - Increasing the charge on particle B. - Moving particle B towards particle A.

Example of what would increase the velocity of the wave?

An example could be for a wave on a string, increasing the modulus of the elasticity.

A wave of light proceeds from object X and strikes the front side of a convex mirror. What image is formed?

Behind the mirror and it is upright.

A positive charge is held at point A, close to another fixed positive charge and then released. The charge is allowed to accelerate for a few moments and then stopped at point B. Which of the following best describes the change in voltage?

Charge doesn't change from point A to point B, the increase or decrease in voltage depends on potential energy. Two particles that repel each other have the most potential energy when they are closest together, so going from point A to point B voltage decreases.

A 2.0 C charge is pushed against a 12.0 V/m constant electric field for a distance of 10 mm. What is the potential energy gained by the particle?

Equation for potential energy would be U = qEd; U = 2(12)(10) = 240 J

Example: What will increase the capacitance of a parallel plate capacitor?

Example: Increase by: - Changing the thickness of plates. - Increasing the polarity of the dipoles in the dielectric. - Doubling the length of the plates. If you move the plates further apart, then it will decrease capacitance

What increases kinetic friction experienced by a block sliding across a horizontal surface?

Following can increase it: - An increase in the acceleration due to gravity. - Increasing uK, the coefficient of kinetic friction. - Increasing the mass of the block.

A man stands 1,000 meters in front of a sheer rock wall. He directs a wave with a wavelength of 0.5 meters at the wall and measures the time, t, required for the wave to return to a detector. If t = 1 second, what is the frequency of the wave?

Given: 1000 m in front; wavelength is 0.5 m; and time is 1 second; frequency? Step 1: Since it takes 1000 meters to go back, and then forth will be double which is 2000 m; and since it travels 1 second, so it will be 2000 m/s back and forth. Step 2: Wave Speed Equation: - V = Fλ; Step 3: Rearrange to get F; it will be V/λ = F, and plug in chug: - F = V/λ; - F = 2000/0.5 = 4000 Hz.

A child is playing with a string attached to a wall and creates a standing wave. If the string is 0.1 meters long and the speed of waves on this string is known to be 100m/s, what is the frequency of the first harmonic?

Given: String is 0.1 meter; speed of waves of string is 100 m/s; frequency? Step 1: We are looking for the first harmonic, which is always 2x of the string length. - 2(0.1) = 0.2m Step 2: Wave speed equation: - V = Fλ Step 3: Rearrange to get F; so it will be V/λ = F, Plug in chug: 100/0.2 = 500 Hz

A jogger is running along the side of a railroad track when he sees a train approaching him. The train blows its whistle with a frequency of 440 Hz. If the jogger is running at 6 m/s, and the train is moving at 50 m/s, which of the following best approximates the observed frequency of the train whistle with respect to the jogger? (Note: assume speed of sound = 350 m/s)

Given: Train whistle frequency is 440 Hz; Jogger running is 6 m/s; and train moves at 50 m/s. C is speed of sound is 350 m/s. Observed frequency? Step 1: Identify the givens and what we need then think of equation to use. - Equation to use: Doppler: Δf/fs = v/c - Rearrange to find Δf. Step 2: Rearranged. - Δf = vf/c; Step 3: Plug in chug: - Δf = 56(440)/350 - Δf = 70 Hz; Step 4: Asking for frequency of train whistle with respect to jogger, so it will be 70 + 440 = 510 Hz.

Two small parallel plate capacitors have identical properties and are connected to one another by a conducting wire. Both capacitors are connected to a circuit containing a battery and a resistor. If the voltage across each capacitor is 20 V and the capacitance of each is 10 C/V, what is the total potential energy stored in the two-capacitor system?

Givens: 20 V is voltage' capacitance is 10 C/V, Potential energy = ?. Step 1: Identify the givens and what we need then think of equation to use. - Equation to use: PE = 1/2 CV^2. Step 2: plug in chug: - PE = 1/2 CV^2 = 1/2(10)(20^2) = 4000J or 4kJ

A ukulele is a very small version of a guitar. The string length of a certain ukulele is 0.3 m. If the speed of waves on the ukulele strings is 10 m/s, what is the frequency of the third harmonic?

Givens: Length of string: 0.3m, speed is 10 m/s, and frequency? Step 1: Length of the string is 2x; - 2(0.3) = 0.6m Step 2: Wave speed equation: - V = Fλ Step 3: Rearrange to get F; so it will be V/λ = F, Plug in chug: 10/0.6; but remember they need third harmonic, which has 3 times the frequency, so it will be: 3V / λ = F; F = 3(10)/0.6 = 50 Hz

For the combustion reaction of the sample into CO2 (g) and H2O (g) in the bomb cell?

In the combustion of a solid to a gas, heat is released (ΔH is negative) and the products are more disordered (ΔS is positive).

Optic Characteristics of human Eye?

Includes: - Relaxing the ciliary muscles will increase the focal distance of the eyes lens. - Minimum focal length of the eye increases with age. - Retina recieves a postive, real inverted image.

What would decrease the velocity of a wave?

Includes: - Wave in gas, and gas temp gets lowered. - Wave on a string, increasing the mass per unit length of the string. - Sound wave, decreasing the bulk modulus of the medium

If all variables are constant, what will increase the voltage across a charge capacitor?

Increasing the distance between the plates would cause an increase in this.

If the amplitude of a wave triples, the intensity will:

Intensity = Amplitude^2, 3 amplitude^2 = 9, So, the intensity will increase by a 9 times.

If the wavelength of light coming from the light source in youngs experiment decreases, how does it affect the # of light and dark bands on the screen?

It affect it, cuz both of the numbers would increase.

A ray of light passes from the air into a medium with n = 1.5. If the index of refraction, n, is increased, which of the following will occur to the angle of refraction (measured from the normal) and to the velocity of the wave, respectively?

It becomes denser, so both the angle of refraction and the velocity will decrease. All waves SLOW DOWN when they hit a denser medium or when "n" increases.

The electromagnetic (EM) spectrum classifies?

It classifies EM waves by frequency or wavelength. Objects with high energy have a higher temperature and emit EM waves with relatively higher frequencies and energy.

A cable with a tension of 45 N is used to suspend a 5 kg mass M against a wall. What is the magnitude and direction of the force of friction between the mass and the wall?

It will be 5N upward, cuz 45N already up, and 50N down. Look at image.

With constant temperature, what would increase the resistance in a current-carrying wire?

It would increase by: - Increasing the length of the wire - Decrease the diameter of the wire.

An object is launched with a one-time burst of propulsion away from the surface of a planet with no atmosphere. Which of the following best describes the changes that occur as the object moves away from the planet's surface?

Kinetic Energy is converted into potential energy. Conservation of energy states that any change in kinetic energy is accompanied by an equal and opposite change in potential energy such that the total mechanical energy remains constant. The kinetic energy of an object launched upward in gravity is converted into gravitational potential energy.

When the angle of inclination of the ramp increases, what happens to kinetic friction?

Kinetic friction decreases because the weight component perpendicular to the ramp decreases.

Adiabatic processes?

Occurs with no heat exchange between the system and the environment.

A man stands on the shore of a lake watching ripples on the water. If 1.4 seconds pass between the time one crest passes him and the time the next crest passes him, what is the frequency of the wave formed on the water?

Period is inverse to frequency, so the inverse of 1.4 = frequency. I can do 1.4^-1 = 0.71 or 1/1.4 = 0.71

An object X is located on the front side of a converging lens beyond the focal length, f. Which of the following describes the image made by the lens?

Positive, Real and Inverted (upside down) (PRI)

A 20 Coulomb charged particle is dropped into a parallel plate capacitor with very large and distant plates, and experiences a force of 250 N. The distance between the plates is 2.0 meters. What is the voltage across the capacitor?

Step 1: Looking to get voltage, which is V = Ed. We need E, so we can't use it just yet. Step 2: Use F = qE; to get E, so it will be: - F/q = E; 250/20 = 12.5; Step 3: Use the voltage equation: V = Ed; V = 12.5 x 2 = 25V

An object of mass 500 kg is sliding across a flat surface due to a horizontal rope pulling it with a tension of 1,000 N. If the coefficient of kinetic friction between the block and the surface is 0.05, and the coefficient of static friction is 0.09, what is the acceleration of the object?

Step 1: Get normal force: - F = mg - F = 500(10) - F = 5000 N Step 2: Since object is moving we deal with kinetic friction, multiply with normal force. - 5000 x 0.05 = 250 Step 3: Get net force - (1000 - 250) = 750N Step 4: Get acceleration. F = ma - a = F/m - a = 750/250 = 1.5 m/s^2

A factory employee is attempting to move a 100 kg crate from the floor to a table 2 m off the floor. The maximum pushing, lifting, or pulling force of which he is capable is 200 N. If he were to construct a ramp to assist him, what is the minimum ramp length that will allow him to accomplish the task?

Step 1: How much force is there. (F = mg) - F = 100(10) - F = 1000 N Step 2: What is he capable of? - F = 200 N Step 3: Factor between the two values? - 1000/200 = 5 Step 4: Hypotenuse of the ramp must be 5 times longer than the height, which is 2 meters. - 5 x 2 = 10m

What is the intensity in W/m2 of a 40 Decibel whistle? (I0, the threshold of human hearing is defined as 1.0 x 10^-12 W/m2)

Step 1: Intensity in Decibels = 10 x log(I/Io) - Log I = the decibel of the wistle = 40 or 10,000, or 1x10^4, - Log Io = given 1x10^-12 10log((1x10^4)/(1x10^-12)) = 1x10^-8 W/m^2

A parallel plate capacitor charged to 4 x 10^-13 C is allowed to discharge for several seconds until it bears a charge of 2.4 x 10^-13 C. How many electrons flowed off of the capacitor during the discharge?

Step 1: What is the charge of an electron? - (-1.6x10^-19C) Step 2: Subtract final charge by initial charge? - (4 x 10^-13 C) - (2.4 x 10^-13 C.) = 1.6 x 10^-13 C. Step 3: Divide it by the charge of an electron: - (1.6 x 10^-13 C) / (-1.6x10^-19C) = 1x10^6

A violin string is fixed at both ends. However, when the person playing the violin presses one of the strings against the neck of the violin, the effective length of the string becomes the distance between the player's finger and the bottom of the string. If a player presses down on a 0.34 meter string 0.10 meters from the top of the string, what is the effective fundamental wavelength of that string? (Note: the speed of waves on the violin string is 120 m/s.)

String Length = 0.34 m, It is pressed at 0.10 from top, so 0.34-0.10 = 0.24 Fundamental Frequency = 2x lenght, so it would be 0.24 (2) = 0.48m

When given 2 coefficient values for kinetic friction, which surface would have the greatest power out of the two, and why? A) 0.4 B) 0.8

Surface B, because it has higher value, which means it transfers more kinetic energy into internal energy per unit time. Higher coefficient of kinetic friction - more power because transfers more kinetic energy into internal energy.

A hand-held calculator uses two small electrodes separated by a distance of 2 cm, with a potential difference of 10 V. If the current across the electrodes is 1.0 x 10^-4 A, how much power is required to run the calculator?

The equation for power is P = IV, I = Current, V is volts. Both are given. plug in chug. P = (1x10^-4)(10) = 1x10^-3 or 1mV

A ray of light travels through air, bounces off of a stationary ideal reflector, and travels back toward its origin. Which of the following is the same before and after reflection of the light ray?

The following will stay the same since it is ideal, which means there is no loss of energy or intensity. I. Frequency II. Wavelength III. Intensity IV. Amplitude V. Speed If this was not ideal, there would be loss in amplitude and intensity.

Resistors vs Capacitors?

The ratio of currents between two are equaled to the inverse of the ratio to their resistance. So if Resistor A has 2, and Resistor B has 1 ohm, it will be 2:1 ohm, but the current would be the inverse a - b (1:2 amps)

An electromagnetic wave traveling in air encounters a medium with n = 1.5. Which of the following is the same in both mediums?

The same would be Frequency.

What is the strength of the electric field between the two electrodes described in the previous question

The strength of the electric field between the two electrodes would be Volt over meters (v/m) or (N/c). Previous questions mentioned that it had 10V, and the distance was 2 cm. Step 1: Convert 2 cm to meters, it will be 0.02 m Step 2: V/m = 10/0.02 = 500 N/C

When 2 waveforms share the same phase, they must also share what?

They must share the same wavelength, frequency, and period.

A man is pushing a crate of mass m with a horizontal force F, at a constant velocity, v, along a sidewalk. A frictional force between the crate and sidewalk opposes the force F. The crate reaches a patch of ice and the coefficient of friction decreases by a factor of 5. Which of the following gives the acceleration of the crate?

This is a hypothetical questions, so we use 1F. Step 1: Friction is reduced by a factor of 5, - So, 1F/5 = 0.2F, Step 2: What is the net force? - (1 - 0.2) = 0.8F Step 3: Solve for F = ma, or a = F/m - a = 0.8F/m

Isochoric (isovolumetric) processes?

This is when the volume of the system does not change.

A star orbiting a black hole in a clockwise direction at a radial distance of 1.0 × 10^6 km is acted upon by a counterclockwise friction force of 250 N perpendicular to the orbit radius. What is the torque on the star?

Torque Formula: T = Frsin(theta), since they mention that it is perpendicular we know that sin(theta) is sin(90 degrees), and if that is 90 degrees it cancels out, leaving T = Fr, so now we just plug and chug, T = (1x10^6)(250) = 2.5x10^11 in counterclockwise direction. - It is counterclockwise cuz the translation force is counterclockwise.

What is the wavelength of a 340 Hz sound produced by a violin? (Speed of sound = 340 m/s)

V = λF, λ = v/f λ = 340/340 = 1m

A 100kg diver jumps directly off a cliff and into the water below. Immediately before hitting the water, his speed is 50 m/s. He continues to a depth of 10 m before being slowed to a stop by the water. Calculate the average force exerted on the diver by the water.

When dealing with average force, we know it is work. Work is change in energy (any type). W = ΔKE. KE = 1/2mv^2 = 0.5(100)(50^2) = 125,000 N. We also know that they asked for force and with work would be W = Fd; F = W/d; 125,000/10 = 12,500 N

A switch is closed and a small amount of current is allowed to pass through a wire. A fraction of a second after the switch is closed, an electron near the end of the wire is inspected. This electron is most likely:

located within the valence of some atom within the wire, having just been displaced from the valence of a neighboring atom within the wire. The first electron to enter the wire will displace an electron in the valence shell of the first atom it encounters. The electron displaced will then displace an electron in a neighboring atom, and so on.

Sound-proof booths are usually constructed of thick glass. Sound cannot be heard outside of the booth primarily because:

the intensity of the sound waves is decreased below the threshold of hearing due to reflection of sound waves off of the glass.