Electron diffraction shows
a. that electrons behave like waves
b. the photoelectric effect
c. characteristic x ray spectra
d. that electrons in atoms have only certain allowed energies
A
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Exhaust gases having properties similar to dry air enter a thin-walled cylindrical exhaust stack at 800 K. The stack is made of steel and is 8-m-tall and 0.5 m inside diameter. If the gas flow rate is 0.5 kg/s and the heat transfer coefficient at the outer surface is 16 W/(m2 K), estimate the outlet temperature of the exhaust gas if the ambient temperature is 280 K.
GIVEN
• Gas properties are similar to dry air
• Gas entrance temperature (Tb,in) = 800 K
• Length of stack (L) = 8 m
• Diameter of stack (D) = 0.5 m
• Mass flow rate (m
) = 0.5 kg/s
• Heat transfer coefficient on the outer surface ( h ,c o ) = 16 W/(m2 K)
• Ambient temperature (T?) 280 K FIND
• The outlet temperature of the exhaust gas (Tb,out)
ASSUMPTIONS
• Radiation heat transfer is negligible
• Natural convection can be neglected
• The inlet to the stack is sharp-edged
• Thermal resistance of the stack wall is negligible
SKETCH
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A ball is thrown horizontally from the top of a tower at the same instant that a stone is dropped vertically. Which object is traveling faster when it hits the level ground below if neither of them experiences any air resistance?
A) It is impossible to tell because we do not know their masses. B) the stone C) the ball D) Both are traveling at the same speed.
Wave 1 has intensity 9.0 units while wave 2 has intensity 4.0 units. What is their ratio of amplitudes,
A1/A2? A. 20 B. 5.1 C. 2.3 D. 1.5 E. 1.3