Two light sources individually provide intensity Io at a point. If the sources are operated at the same time and are coherent but out of phase 30°, what is the intensity at that point?
A)
3.7 Io
B)
2.0 Io
C)
3.0 Io
D)
2.8 Io
E)
1.0 Io
A
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A large high-power transformer is installed and operated in an electric-power distribution station. To maintain transform efficiency and prevent its failure (burnout), the transformer oil is cooled via a water-cooled, coiled tube heat exchanger and circulated through the transformer winding module. For one such application, transformer oil, with a flow rate of 0.3 kg/s, is to be cooled to 30°C while flowing through the coiled thin walled metallic tubing. The tube has an inner diameter of 5.0 cm, and its surface is maintained uniformly at a temperature of 20°C. If the oil enters the heat exchanger tube at a temperature of 50°C, and if the coil effects can be ignored and tube modeled as a straight circular pipe, what is the tube length required for this heat exchanger? What is the
expected pressure drop across the tube length? Also, if the tube surface temperature increases to 25°C, determine the outlet temperature of transformer oil for the calculated pipe length.
GIVEN
• Transformer oil cooled via water-cooled, coiled tube heat exchanger.
• Oil flow rate, m = 0.3 kg/s.
• Oil inlet temperature, Tb,in = 50°C.
• Oil outlet temperature Tb,out=300C
• Inner or inside diameter of pipe in which oil flows, D = 5 cm = 0.05 m.
• Temperature of pipe surfaceTs = 20°C.
FIND
• Length of tube required for heat exchanger
• Oulet temperature is surface temperature reaches to 250C for given length.
ASSUMPTIONS
• The temperature of wall is constant and uniform across the length of pipe.
• The thermal resistance of the pipe is negligible, and hence the inside surface temperature of the pipe is Tw = Ts, this represents a uniform pipe surface temperature condition.
SKETCH
In a situation where an object can move only along the x axis, a book states “the force on the object is F = -kx, where k is a constant, and x is the object’s position coordinate.” Is F being used here as a shorthand symbol for 
(A) or Fx (C)?
A. A B. C
A wooden raft has a mass of 55 kg. When empty it floats in water (density with 64% of its volume submerged. What maximum mass of sand can be put on the raft without sinking it?
What will be an ideal response?
Mars, Jupiter, Saturn, and Venus are the Jovian planets.
a. true b. false