A 150-V battery is connected across two parallel metal plates of area 28.5 cm² and a separation of 8.20 mm. A beam of alpha particles (charge +2e, mass 6.64E-27 kg) is accelerated from rest through a potential difference of 1.75 kV and enters the region between the plates perpendicular to the electric field.

What magnitude and direction of magnetic field are needed so that the alpha particles emerge undeflected from between the plates?

A boxed 15.0 kg computer monitor is dragged by friction 6.50 m up along the moving surface of a conveyor belt inclined at an angle of 36.8 ∘ above the horizontal. If the monitor's speed is a constant 3.00 cm/s , how much work is done on the monitor by friction, gravity, and the normal force of the conveyor belt?

Wfriction =

Wgravity =

WN =

3) A piece of metal with a mass of 3.8 kg and density of 1808 kg/m3 is suspended from a string and then completely immersed in a container of water. The density of water is 1000 kg/m3 .
(a) Determine the volume of the piece of metal.
(b) Determine the tension in the string after the metal is immersed in the container of water.

SHOW ALL WORK AND FORMULAS! THANKS!

A skydiver, weighing 180 lb (including equipment) falls vertically downward from an altitude of 4000 ft and opens the parachute after 10 s of free fall. Assume that the force of air resistance, which is directed opposite to the velocity, is of magnitude 0.75|v| when the parachute is closed and is of magnitude 10|v| when the parachute is open, where the velocity v is measured in ft/s. (A computer algebra system is recommended. Use g = 32 ft/s2 for the acceleration due to gravity. Round your answers to two decimal places.)

(a) Find the speed of the skydiver when the parachute opens.

(b) Find the distance fallen before the parachute opens.

(c) What is the limiting velocity v_L after the parachute opens?

(d) Determine how long the sky diver is in the air after the parachute opens.

e) Plot the graph of velocity versus time from the beginning of the fall until the skydiver reaches the ground.

Suppose that a car oscillates vertically as if it were a mass of m = 800 kg on a single spring with spring constant k = 7 × 104 N/m which is attached to a single damper with c = 3000 N·s/m. Suppose that this car is driven along a sinusoidal road surface with an amplitude of 5 cm and a wavelength of L = 10 m.

1.Write the non-homogeneous ODE that governs the vertical motion of the car. (Make sure to keep track of units).

2. Find the steady-state amplitude of vibration of the car as a function of the horizontal driving speed v (m/s).

3. At what driving speed vm will the greatest amplitude of vertical vibrations occur?

4. If the driver would prefer that the car oscillates with a lower amplitude than that of the underlying road surface (i.e. A < 5 cm), in what range of speeds must they drive?

at the local county fair, you watch as a blacksmith drops a 0.50kg iron horseshoe into a bucket containing 25kg of water. If the initial temperature of the horseshoe is 450C and the initial temp of water is 23C, what is the equilibrium temp of the system?

Do equipotential lines get closer together or further apart at a sharp corner of a cconductor? what about the electric field lines? What does this indicate about the electric field strength in this region?

A spherical weather balloon is filled with hydrogen until its radius is 3.40 m. Its total mass including the instruments it carries is 11.0 kg.

(a) Find the buoyant force acting on the balloon, assuming the density of air is 1.29 kg/m³.
_________N

(b) What is the net force acting on the balloon and its instruments after the balloon is released from the ground?
_________N

Two point charges lie on the x axis. A charge of -2.3 x 10-6 C is at x=-5 cm, and a charge of +9.2 x 10-6 C is at x=12 cm. At what position x would a third positive charge be in equilibrium?

The greater the speed of a satellite, the shorter its orbital period. T/F

Reading this PE question can-we-transport-energy-over-infinite-distances-through-vacuum-using-light, a related question arises naturally:

Is energy transported (by light)? -- (I did believed in this answer until now) or energy is already 'in site' (vacuum) just expecting to be excited by the photons?

This news insinuated the doubt anti-laser(1)

The antilaser does the reverse: Two perfect beams of laser light go in, and are completely absorbed.

If vacuum is able to absorb energy then it can do the reverse, and supply energy. We are already prepared to accept that vacuum has energy.

I am inclined to accept that energy do not travel at all. What is travelling is the excitation of vacuum, and we call this: photons. It may appear a question of semantics, but I think that the explicit reconaissance of this notion can be helpful.

(1) The two rays entering the slab are in phase opposition when they met, and cancel. The nature of cancelation was obscure to me, until now.

added:

I googled this: "where goes the energy in a destructive interference" and followed past answers to this question. Someone answered "into the surrounding environment." We are in minority;) Most of the times they said that the total extinguishing is impossible. This anti-laser experiment shows that energy is destroyed.

We see the same effect with sound cancelation , with boat wake (trailing waves) cancelation (by double/triple hull or when they sail in formation), and now with light.

added after 2 answers
image from astro-canada.ca
What is amazing is that this fact is inside the theory since the begining, quoting from there:

In 1801, the British physicist Thomas Young demonstrated that light propagates as waves, like waves on the surface of water. Young understood that when two light waves meet, they interact with each other. Scientists call this

A conduction electron is confined to a metal wire of length 13.2 cm. By treating the conduction electron as a particle confined to a one-dimensional box of the same length, find the energy spacing between the ground state and the first excited state. Give your answer in eV.

With a plane wave, I always took the direction of the wavevector, k, as the direction of propogation (magnitude proportional to the inverse wavelength). Alternatively, it could represent the momentum (minus a factor ?) of a particle.

However inside a crystal, the electron wavevector and the electron velocity are not necessarily in the same direction. I'm thinking here of a 2D material with a cylindrical Fermi surface where the momentum may have a z component, but the Fermi velocity does not. In everyday cases you would expect momentum and velocity to be in the same direction, moreover I considered the propogation of the wave to be in the same direction as its particle analogue.

I realise that inside a crystal the electrons are no longer simple plane waves, but what then does the k vector mean?

A series RLC circuit consists of a 58.0 ? resistor, a 2.50 mH inductor, and a 450 nF capacitor. It is connected to a 3.0 kHz oscillator with a peak voltage of 5.60 V. What is the instantaneous emf E when i = I ? What is the instantaneous emf E when i = 0A and is decreasing? What is the instantaneous emf E when i = - I ?