The drawing shows an equilateral triangle, each side of which has a length of 3.99 cm. Point charges are fixed to each corner, as shown. The 4.00 C charge experiences a net force due to the charges qA and qB. This net force points vertically downward and has a magnitude of 305 N. Determine (a) charge qA, (b) charge qB.

Public Radio station KXPR-FM in Sacramento broadcasts at 88.9 MHz. The radio waves pass between two tall skyscrapers that are 15.0 m apart along their closest walls.

1) At what horizontal angles, relative to the original direction of the waves, will a distant antenna not receive any signal from this station?

2) If the maximum intensity is 4.00 W/m2 at the antenna, what is the intensity at ±4.00∘ from the center of the central maximum at the distant antenna?

I= W/m^2

1. Fireflies emit light across the visible spectrum, but the peak intensity of their emission is around a wavelength of 550 nm. So let’s make the approximation that all of the light emitted by a firefly has a wavelength of 550 nm. (a) A typical flash of light from a firefly lasts for about 100 ms and has a power of 1.2 mW. How many photons are emitted in each flash. (b) An “electron volt” (eV) is a unit of energy. It is the energy that an electron gains when it “falls through” a potential difference of 1.0 V. What is an electron volt, in Joules. (c) Energy is stored in a firefly’s body (just like in your body) in ATP molecules. The amount of energy provided by metabolizing one ATP molecule is 0.30 eV. How many ATP molecules does the firefly need to metabolize to emit one photon

1.) A fast moving vehicle travelling at a speed of 33.9 m/s comes up behind another vehicle which is travelling at a slower, constant speed of 15.4 m/s. If the faster vehicle does not begin braking until it is 15.8 meters away from the car in front of it, what is the minimum acceleration that the faster car must exhibit if it is to avoid colliding with the car in front? Assume that both cars are travelling in the positive direction. 2.)A college student stands on a balcony of a sorority house a distance of 10.0 meters above the ground. Her sorority sister is on the ground below the balcony, and tosses her keys straight upward toward her friend who catches the keys 4.9 seconds later. With what speed were the keys initially thrown?

Consider a tug of war between two teams. Why is it impossible for either team to pull harder on the rope than the other? If pulling on the rope harder than the opponent is impossible, why is it possible for a team to still win?

On a frictionless horizontal air table, puck A (with mass 0.251 kg ) is moving toward puck B (with mass 0.374 kg ), which is initially at rest. After the collision, puck A has velocity 0.116 m/s to the left, and puck B has velocity 0.652 m/s to the right.

Calculate ΔK, the change in the total kinetic energy of the system that occurs during the collision.

1. a. Which has more potential energy, a 10-kg box on a shelf or a 5-kg box on a shelf that’s twice as high? Explain.

   b. Which has more kinetic energy, a 2000-kg car traveling down the road or a 1000-kg car traveling twice as fast? Explain.

2. If your friend pushes a lawnmower six times as far as you do while exerting one half as much force, which one of you does more work? How much more? Explain.

3. a. A car has a certain amount of kinetic energy when it’s moving at 40 mph. If it speeds up until it’s going at 80 mph (two times faster), how many times more kinetic energy does it have? Explain.

   b. If the stopping distance for the car at 40 mph was about 75 ft, what is the stopping distance when it’s going two times faster? (Assume the stopping force stays the same. Keep in mind that Work, which is force × distance, is equal to the change in kinetic energy.)

4. An apple hanging from a limb has potential energy relative to the ground because of its height. If it falls, what has become of this energy just before it hits the ground? What has become of this energy after it hits the ground? Explain.

5. A roller coaster car has a potential energy of 10,000 J (relative to the ground) at the top of a certain hill, where it’s almost motionless. Then it rolls down the track. Explain your answers to these questions, assuming friction and air resistance can be neglected.

   1. The bottom of the hill is right at ground level. When the car gets there, how much potential energy and how much kinetic energy will it have?

   2. The car goes up another hill which is 3/4 as high as the original hill. How much potential energy and kinetic energy will the car have at the top of this second hill?

   3. The car goes down the second hill, where once again the track reaches ground level. How much potential energy and kinetic energy will the car have there?

A 195 g block is pressed against a spring of force constant 1.55 kN/m until the block compresses the spring 10.0 cm. The spring rests at the bottom of a ramp inclined at 60.0° to the horizontal. Using energy considerations, determine how far up the incline (in m) the block moves from its initial position before it stops under the following conditions.

(a)

if the ramp exerts no friction force on the block

_______m

(b)

if the coefficient of kinetic friction is 0.420

________m

(c)

What If? If the ramp is 4.00 m long, what is the maximum coefficient of friction that would allow the block to reach the end of the ramp?

__________

A long horizontal wire carries a current of 48 A. A second wire, made of 2.7 mm diameter copper wire and parallel to the first, is kept in suspension magnetically 15 cm below. Determine the magnitude of the current in the lower wire. Determine the direction of the current in the lower wire. IS IT IN STABLE EQUILIBRIUM?

Consider an electron confined to an infinite well of width 2ao (Bohr radius). Compare its energy in its three lowest energy states to the three lowest energy states of the Bohr model of the hydrogen atom. Repeat for a proton confined to a well of width 2x10-15 m (a nucleus).

8. Summarize the case for why Pluto should not be considered a planet.

If an electron in an atom has orbital angular momentum with ml values limited by ±2, how many values of (a) Lorb,z and (b) μorb,z can the electron have? In terms of h, m, and e, what is the greatest allowed magnitude for (c) Lorb,z and (d) μorb,z? (e) What is the greatest allowed magnitude for the z component of the electron's net angular momentum (orbital plus spin)? (f) How many values (signs included) are allowed for the z component of its net angular momentum?

can you explain light and matter using physics. Discoveries made by light and matter etc..