please rephrase/ rewrite this paragraph and you can add your own ideas
The idea of using the sun’s energy was thought of the late 1870 when two American scienists became interested in the work of an electrican named willouhby smith who was testing underwater telegraph lines for faults using a material called selenium. Smith realized that electricity travelled through selenium well when it was in light, but it didn’t in the absence of light. It was not long before the scientists discovered that the sun’s energy generates a flow of electricity in selenium. It wasn’t until decade later that Charles Fritts invented the world’s first ever photovoltaic cell. He did this by putting a layer of selenium onto a metal plane and covering it with pieces of gold that had been beaten into thin sheet. Under the light this cell made even more electricity than had been seen with just selenium but not enough to be useful. At the time, photovoltaic technology was contending with other further developed technologies such as hydroelectricity and steam driven generators. Upon hearing of the developments in the field, Albert Einstein committed his studies to understanding the relationship between light and electricity. Building on the work of Plank, Einstein argued that light was actually made of tiny packets of energy that move likes waves. He referred to these ‘’energy packets’’ as photons. He later argued the energy of these photons is wavelength dependent, so the photons at visible wavelengths are more energetic than those of infared.
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please rephrase/ rewrite this paragraph and you can add your own ideas
It has become clear that at this point sustainability is the most important aspect of energy production. Perhaps the most accessible form of renewable energy for the everyday New Yorker at this solar energy. Due to the architectural setup it is difficult for New York citizen to harness energy from a windmill or even a hydro-dam. In more and more NY neighborhoods companies are installing solar panels on the roofs of building in order to store and use the sun energy
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In: Physics
The air pressure inside the tube of a car tire is 353 kPa at a temperature of 14.0 °C. What is the pressure of the air, if the temperature of the tire increases to 63.0 °C? Assume that the volume of the tube doesn't change.
What is the air pressure inside the tube, if the volume of the tube is not constant, but it increases from 21.0 l to 21.9 l during the warming process described above?
In: Physics
Objects with masses of 140 kg and a 440 kg are separated by 0.500 m.
(a) Find the net gravitational force exerted by these objects on a 43.0-kg object placed midway between them.
Magnitude:
(b) At what position (other than infinitely remote ones) can the
43.0-kg object be placed so as to experience a net force of
zero?
m from the 440-kg mass
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(a) Estimate the terminal speed of a wooden sphere (density 0.790 g/cm3) falling through air, if its radius is 7.50 cm and its drag coefficient is 0.500. (The density of air is 1.20 kg/m3.)
[ ] m/s
(b) From what height would a freely falling object reach this speed in the absence of air resistance?
In: Physics
Now consider the collision represented in the animation below. Let's assume that the two balls are sliding on a frictionless, horizontal surface. Do not assume that this collision is elastic (though it might be). Here's what's given:
The direction of +x is to the right.The blue ball has twice the mass of the red. Let's make them mb = 2 kg and mr = 1 kg.
The red ball is initially stationary.
The initial velocity of the blue ball, vbi, is 6 m/s, and its final velocity, vbf, is 2 m/s.
1)Find the final velocity, vrf, of the red ball, in meters per second. Enter only a single number (without units) before submitting. If your answer isn't an integer, you've made a mistake somewhere ! 2)The principle that I used to get the answer to the previous question was conservation of ... 3)
the initial KE of the system (both balls) in this problem is: (give answer and show/explain how you got it) 4)
The final KE of the system (both balls) in this problem is: (give answer and show/explain how you got it) 5) was the collision elastic?
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1. Ablockofmass M = 4kg, cross-sectional area A = 1 m^2, and height h = 60 cm sits in a liquid with density ρ = 12 kg/m^3.
a) Find the depth d the block will sit in the water when in
equilibrium.
b) At time t=0, the block is released from being completely
submerged in the liquid, calculate the amplitude and frequency of
oscillation.
In: Physics
SLIDING OSCILLATIONS 3 My Notes A block weighing 273 g slides along a frictionless track at a speed 8.9 cm/s. It then attaches to a spring-bumper with an electromagnetic device so that the block attaches to the bumper. The bumper has a mass of 115 g, and the spring has a stiffness of 1110 kg/s2 and an equilibrium length of 9.5 cm. After the spring compresses and returns to its original length, the magnet turns off and the block launches off again, conserving energy. (a) How fast is the block just after it attaches to the paddle? (b) What is the maximum compression of the spring before the block turns around? (b) How fast is the block moving after it launches off the paddle?
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A transverse sinusoidal wave on a string has a period T = 33.0 ms and travels in the negative x direction with a speed of 30.0 m/s. At t = 0, a particle on the string at x = 0 has a transverse position of 2.00 cm and is traveling downward with a speed of 3.00 m/s. (a) What is the amplitude of the wave? m (b) What is the phase constant? rad (c) What is the maximum transverse speed of the string? m/s (d) Write the wave function for the wave. (Use the form Asin(kx + ωt + ϕ). Round all coefficients to three significant figures.) y(x, t) =
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A very light string is wound around a cylindrical spool of inertia M and radius R. The cylinder rotates on a frictionless horizontal axis with a moment of inertia 1 2MR2 . Attached to the end of the string is a block of inertia m, which pulls on the string and unwinds it from the cylinder, as the block falls.
(a)Draw an extended free-body diagram for the cylinder, and a regular free-body diagram for the block.
(b)Let m = 5 kg, M = 2 kg, and R = 6 cm. What is the acceleration of the block as it falls?
(c)What is the tension on the string
(d) After the block has dropped 30 cm, starting from rest, what is the total kinetic energy of the system, and how is it distributed between the block and the cylinder?
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A heat engine receives an amount of energy Qh= 790 kJ by heat transfer from a high temperature thermal reservoir at Th=950 K. Energy is rejected by heat transfer to a lower temperature thermal reservoir at T1=590 K. If waste heat in the amount of Q1=160 kJ is rejected to the low temperature thermal reservoir during each cycle.
a) Solve for the maximum theoretical efficiency that an engine in this situation could operate with. ANSWER: 0.379
b) Solve for actual efficiency that the engine is operating with.
c) Which of the following best describes the manner in which the cycle is operating...
-Reversibly or Impossibly?
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The two blocks, m1 = 2.6 kg and m2 = 4.2, in the figure below are connected by a massless rope that passes over a pulley. The pulley is 12 cm in diameter and has a mass of 2.0 kg. As the pulley turns, friction at the axle exerts a torque of magnitude 0.55 N · m. If the blocks are released from rest, how long does it take the 4.2 kg block to reach the floor from a height of h = 1.0 m? (Note: If your random numbers do not create movement between the masses enter 0 for your answer.)
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A simple pendulum of length 0.50 m has a 0.30-kg bob. At t = 0, the bob passes through the lowest position in its motion, and at this instant it has a horizontal speed of 0.39 m/s . A. What is the maximum angular displacement ϑmax away from vertical that the pendulum reaches? B. What is the magnitude of the bob's linear speed v when it has angular displacement ϑmax/2?
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Which of the descriptions below is an example of resonant energy transfer? (Choose all that are correct.)
View Available Hint(s)
Hint 1.
opened hint
Review natural frequency and resonance.
Which of the descriptions below is an example of resonant energy transfer? (Choose all that are correct.)
| A block sliding on a horizontal surface slows down and comes to a stop due to the friction force. |
| Soldiers marching in unison on a bridge with their steps at a frequency that is very different than the natural vibration frequency of the bridge. |
| A vibrating pendulum connected to a very similar second pendulum influences the vibration of the second pendulum. The amplitude of vibration of the first pendulum decreases and the amplitude of the second increases. This exchange of amplitude and energy keeps happening back and forth between the two pendulums. |
| Ultrasound machines are used to apply a variable force at a frequency that matches the natural frequency of gall stones, causing the gall stones to vibrate and break up. |
| A box is pushed with a constant force down an empty abandoned hallway and its speed increase. |
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During typical urination, a man releases about 400 mL of urine in about 30 seconds through the urethra, which we can model as a tube 4.0 mm in diameter and 20 cm long. Assume that urine has the same density as water, and that viscosity can be ignored for this flow. What is the flow speed in the urethra? If we assume that the fluid is released at the same height as the bladder and that the fluid is at rest in the bladder (a reasonable approximation), what bladder pressure would be necessary to produce this flow? (In fact, there are additional factors that require additional pressure; the actual pressure is higher than this.)
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