Since force is m*a, it has units of kg m/s^2 . Energy has units of kg m^2/s^2. Thus it appears that by lazy dimensional analysis that a force times a distance will have units of energy. This turns out to be the formula to calculate work. Note also that kg m^2/s^2 looks like mv^2. Here if we use dimensional analysis, we would *almost* find the formula for kinetic energy. We'd be off by a factor of two since KE=1/2 mv^2. Note that this would still be useful for estimation (such as we did the first few weeks).

1) Describe Bohr’s quantum model of the atom.

2) Derive expressions for the energies and radii of an electron in the hydrogen atom.

3) Discuss experiments that confirmed the existence of quantized atomic energy levels.

My physics class did an online lab thing where a charged plastic rod is brought near a magnetic and non-magnetic conduction rod about the same size. Both ends of the magnet and the non-magnetic rod were attracted to the charged rod. I am a little confused and what forces/ different forces are causing this

Question: If the charged rod is attracted to the magnetic and the non-magnetic rod in the same way, can you conclude that there are any special interactions or forces between either of the magnetic poles and the rod?

Question: Is the interaction between magnets a different phenomenon from the electrostatic interaction of charges? Cite evidence for your answer (use question 2 to help). Keep in mind we are talking about electrostatics i.e. the charges are not moving, NOT electrodynamics where charges are in motion.

Find the net torque on the wheel in the figure below about the axle through O perpendicular to the page, taking a = 5.00 cm and b = 23.0 cm. (Indicate the direction with the sign of your answer. Assume that the positive direction is counterclockwise.) N · m A wheel rotating about an axle is approximated as two concentric circles with the center defined to be O. The radius of the inner circle is a and the radius of the outer circle is b. Three arrows representing individual forces are as follows. An arrow labeled 12.0 N acts on the top left of the inner circle, and points down and to the left at an angle of 30.0° below the horizontal. An arrow labeled 10.0 N acts on the top of the outer circle and points to the right. An arrow labeled 9.00 N acts on the right of the outer circle and points down.

To find the height of an overhead power line, you throw a ball straight upward. The ball passes the line on the way up after 0.85 s , and passes it again on the way down 1.5 s after it was tossed.

a) What is the height of the power line?

b) What is the initial speed of the ball?

Refractive index of core of an optical fibre is 1.46 and its diameter is 250μm. Light propagates along the axis of the fibre . If the fibre bends at one point with radius of curvature R, Calculate the minimum value (critical radius of curvature R_min) to sustain the light inside, without escaping from the fibre.

Discuss the factors on which the critical radius of curvature may depend? Does it depend on the colour of light propagating through the fibre?   

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6. Electromagnetism

a. Describe two ways to increase the strength of an electromagnet

b. Write two or three sentences to identify the energy conversion that takes place in an electric motor and to describe how electromagnetism is involved.

c. Write two or three sentences to compare the primary and secondary coils in a step-down transformer and to explain how electromagnetism is involved in its function.

d. What is the magnetic force on a particle that has -3.2 x 10^-19 C of charge and is moving at 2.5 x 10^7 m/s to the right through a magnetic field that is 0.24 T and pointing away from you? Specify both magnitude and direction in your answer.

1.Explain how a solenoid works - how does it produce a magnetic field?

2. What are the five major types of magnetic materials? Describe each briefly.

A metal marble is launched with a speed of v0 = 30.0m/s at 5.0 ◦ relative to the horizontal, from a height of 1.0 m above ground, and towards a very tall vertical wall, which is 6.0 m away from the launch position. The projectile may first hit the wall, or the ground. Whichever it turns out to be, assume that this is an elastic, specular collision, so that the projectile bounces off. After some time, the projectile will have another collision, which again could be either with the ground or with the wall.

Find: (a) the location of the second collision; (b) the highest point (both the x- and the y-coordinates) that the projectile reaches between its launch and the second collision; (c) the velocity (the magnitude and the angle relative to the vertical—make a sketch so that it is clear which angle you are reporting) 0.50 s after launch.

A sample of radioactive materials emits 1 MeV gamma rays and has an activity of 23 curies, How long can a radiation worker be exposed to the affected area before exceeding the annual exposure limit of 5 rem? The worker is in direct contact with the sample.

A car is parked on the side of the road with the radio playing. Physics students in the car measure the sound coming from the radio to be 18.2 kHz. Another physics student is riding a bike and moving towards the car at 30 km/h.

a) What is the frequency of the radio as heard by the physics student riding the bike?

b) The physics student riding the bike passes the car and starts to move away from the car. What now, is the frequency of the radio as heard by the physics student riding the bike?

Please help me with this.

Qualitative practice with systems

For the following situations, determine whether the energy of the given system is the same at the initial and final states indicated (i.e., is the energy of the system constant or not).

0pts
0pts

A block is hung from a spring that is vertical and connected to the ceiling. The block is made to oscillate vertically. Call the initial state when the block is at its highest position and the final state when the block is at its equilibrium position.
Energy of the system is constant Energy of the system is not constant  System: block
Energy of the system is constant Energy of the system is not constant  System: block + ceiling (+ spring) + Earth
Energy of the system is constant Energy of the system is not constant  System: block + Earth

A block on a table (friction between the table and the block is not negligible) is attached to a wall via a spring that is horizontal. You give the block a brief push so that the block travels horizontally. Call the initial state when the spring first reaches its maximum stretch in the initial direction of motion. The final state is when the spring first reaches its zero stretch length.
Energy of the system is constant Energy of the system is not constant  System: block + wall (+ spring) + table
Energy of the system is constant Energy of the system is not constant  System: block + wall (+ spring)
Energy of the system is constant Energy of the system is not constant  System: block + table
Energy of the system is constant Energy of the system is not constant  System: table
Energy of the system is constant Energy of the system is not constant  System: block

1pts

0pts

A person wearing roller skates is standing in front of a wall. Assume that the wheels on the skates are good enough that they roll ideally. The person pushes off the wall and begins traveling away from the wall. Call the initial state when the person was standing at rest in front of the wall with her hand touching the wall. The final state is when she has traveled 2 m away from the wall and is moving at a constant speed of 0.69 m/s.
Energy of the system is constant Energy of the system is not constant  System: girl+wall
Energy of the system is constant Energy of the system is not constant  System: wall
Energy of the system is constant Energy of the system is not constant  System: girl

A person is jumping on a trampoline. After coming off of the trampoline, he is in the air for 1.4 seconds. Call the initial state when the trampoline is at its lowest point with the person still on the trampoline. The final state is 0.8 seconds after the person comes off the trampoline.
Energy of the system is constant Energy of the system is not constant  System: girl + Earth
Energy of the system is constant Energy of the system is not constant  System: trampoline
Energy of the system is constant Energy of the system is not constant  System: girl
Energy of the system is constant Energy of the system is not constant  System: girl + trampoline
Energy of the system is constant Energy of the system is not constant  System: girl + trampoline + Earth

1pts

You push a box up a ramp (friction between the box and the ramp is not negligible). Call the initial state when you begin to push the box. Call the final state after you have pushed the box up the ramp a distance of 0.5 m and it is moving with a speed of 2 m/s
Energy of the system is constant Energy of the system is not constant  System: you
Energy of the system is constant Energy of the system is not constant  System: box + ramp + Earth + you
Energy of the system is constant Energy of the system is not constant  System: box + ramp
Energy of the system is constant Energy of the system is not constant  System: box + ramp + Earth
Energy of the system is constant Energy of the system is not constant  System: box

Two cars are driving down the road. They notice that they are going to crash, so both drivers slam on the brakes. The cars skid, but still collide. The cars stick together and eventually slide to a stop. Call the initial state just before the drivers apply the brakes and the final state just after the collision had occurred. Treat this situation as realistically as possible.
Energy of the system is constant Energy of the system is not constant  System: the first car
Energy of the system is constant Energy of the system is not constant  System: both cars
Energy of the system is constant Energy of the system is not constant  System: the second car
Energy of the system is constant Energy of the system is not constant  System: both cars + the ground

Question 1: Electrostatics

a. Draw the electric field lines around a system that consists of two equal positive charges

b. Calculate the electric force that exists between two objects that are 7.3 x 10^-2 m apart and carry charges of 4.5 x 10^-6 C and -7.2 x 10^-6 C. Is this force attractive or repulsive?

c. Write two or three sentences to explain the effect on the electric force between two charged objects if the amount of charge on one of the objects is doubled at the same time as the distance between the objects is doubled.

A 3.61 kg particle has the xy coordinates (-1.06 m, 0.516 m), and a 3.39 kg particle has the xy coordinates (0.820 m, -0.0640 m). Both lie on a horizontal plane. At what (a) x and (b) y coordinates must you place a 2.60 kg particle such that the center of mass of the three-particle system has the coordinates (-0.672 m, -0.106 m)?

Q4. Tiger Woods is known for having one of the fastest driving swings in Golf (among other things). In fact, his Tee-off ball speed was recorded to be 122 MPH.

1. Determine what Tiger Wood’s angular velocity and acceleration are for the club. He is 1.85 meters tall. (Refer to the Anthropometry slides to estimate his shoulder height)

Shoulder height = 1.5133

122 MPH = 54.54 m/s