2) A steel rod with a cross-sectional area of 0.25 sq. in. is stretched between two fixed points. The tensile load at 70 degrees F is 1200 lb. What will be the stress at 0 degrees F? At what temperature will the stress be zero?

Assume ? = 6.5 x 10^-6 °F^-1 and E = 30 x 10⁶ psi.

1. Write a couple (2) of paragraphs describing the origin of both the continuous background spectrum and the dark lines in the solar spectrum.

The Sun rotates around the center of the Milky Way Galaxy (the figure below (Figure 1)) at a distance of about 30,000 light-years from the center (1ly=9.5×1015m). 1.If it takes about 200 million years to make one rotation, estimate the mass of our Galaxy. Assume that the mass distribution of our Galaxy is concentrated mostly in a central uniform sphere. Express your answer using one significant figure. 2.If all the stars had about the mass of our Sun (2×1030kg), how many stars would there be in our Galaxy? Express your answer using one significant figure.

1.

If it takes about 200 million years to make one rotation, estimate the mass of our Galaxy. Assume that the mass distribution of our Galaxy is concentrated mostly in a central uniform sphere.

Express your answer using one significant figure.

2.

If all the stars had about the mass of our Sun (2×1030kg), how many stars would there be in our Galaxy?

Express your answer using one significant figure.

physical therapists are often contracted to certify that firefighters are able to do task that model what they must be able to do when firefighting. in one task, a firefighter must thrust a 20 pound weight horizontally so that it lands at least 18 feet away. if the firefighter has a shoulder height of 4.5 feet, what is the minimum speed in feet/s at which the weight must be thrown?

(1) Radio waves and light are electromagnetic waves and transverse waves that can operate in a medium or in space.

What is an Aether or ether?

Upon which medium does sound travel the fastest?

(2) Some scientists think that ether does exist but does exist in another dimension that we cannot see. Can you elaborate on this?

A person with mass m= 70 kg takes the elevator to the top of the Empire State Building at a height of 300 m. Assum the elevator takes 1 min to reach the top of the building

(a) Find the work done on the person by gravity during the elevator ride?

(b) Find the amount of work the normal force of the floor did on the person.

(c) Find the average power of the force of gravity.

One of the many isotopes used in cancer treatment is gold ¹⁹⁸₇₉Au, with a half-life of 2.70 days. Determine the mass of this isotope that is required for an activity of 213 Ci.

Explain why the resonance frequency is a double of the driven frequency of the signal generator.

part a) When a 5.0-μF capacitor is connected to a generator whose rms output is 31 V, the current in the circuit is observed to be 0.25 A. What is the frequency of the source? (answer must be in Hz)

part b) An inductor has a 58.4-Ω reactance when connected to a 60.0-Hz source. The inductor is removed and then connected to a 47.0-Hz source that produces a 115-V rms voltage. What is the maximum current in the inductor? (answer must be in A)

part c) A sinusoidal voltage

Δv = (50.0 V)sin(180t)

is applied to a series RLC circuit with

L = 50.0 mH,

C = 170.0 μF,

and

R = 50.0 Ω.

(a) What is the impedance of the circuit in Ω?

(b) What is the maximum current in the circuit in A?

In the Bohr model, the Paschen series of spectral lines is caused by radiation absorbed or emitted as an electron transitions between the 2nd excited state and any higher excited state (3rd excited state and higher) of the hydrogen atom. The Paschen series spectral lines all involve infrared photons.

a) Using the Bohr model, calculate the energy of the electron when it is in the 2nd excited state, in units of electron-Volts (eV).

b) Calculate the energy of the electron when it is in the 3rd excited state, in units of eV.

c) Calculate the energy difference between the 2nd and 3rd excited states, in units of eV.

d) Suppose the electron falls from the 3rd excited state to the 2nd excited state. Calculate the wavelength of the radiation that is emitted in this transition. This is known as the Paschen alpha spectral line.

A motorcycle is following a car that is traveling at constant speed on a straight highway. Initially, the car and the motorcycle are both traveling at the same speed of 21.0 m/s , and the distance between them is 60.0 m . After t1 = 4.00 s , the motorcycle starts to accelerate at a rate of 7.00 m/s2 . The motorcycle catches up with the car at some time t2.

B) How long does it take from the moment when the motorcycle starts to accelerate until it catches up with the car? In other words, find t2−t1.

C) How far does the motorcycle travel from the moment it starts to accelerate (at time t1) until it catches up with the car (at time t2)? Should you need to use an answer from a previous part, make sure you use the unrounded value.

A see-saw made from 4 meter board sits on a pivot at its center. A child weighing 280 N sits 1.75 m away from the center. A second child who weighs 330 N sits on the other side such that the board remains horizontal and steady.

Now you come and push on the end of the seesaw nearest the second child with a force of 110 N. You don’t push straight up, but at an angle of 25° from the vertical – tilted a bit toward the center of the seesaw. The first child moves to maintain equilibrium.

(d) Based on your intuition, which way should the child move? Towards or away from the center?

(e) Calculate how far she is now from the center?

(f) What is the force now (magnitude and direction) that the pivot applies to the board?

1. An 8kg mass is observed traveling with a speed of .08*c.

What is its classical momentum?

What is the relativisitic momentum?

What is the difference between the two values?

Repeat the problem for a speed of .2*c and .8*c

If you travel by starship to the center of the galaxy such that you arrive within a subjective human lifespan, how much radiation damage will you suffer from the interstellar vacuum?

Assume special relativity holds and ignore the problems of accelerating and decelerating the spacecraft.

At what point in the journey through the interstellar vacuum would you will suffer too much radiation damage to go on?

How did you determine the amount of radiation damage? What equations did you need? What values did you use for the variables? How did you determine those values?