An astronaut on the Moon drops a feather and a hammer at the same time. Which hits the ground first?
A. The hammer hits first due to its larger mass.
B. The feather hits first since there is no air resistance on the Moon.
C. The feather hits first due to the decreased weight of the hammer.
D. The feather and the hammer hit the ground at the same time.
Answer: D
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Ideal Gas Law: On a cold day, you take in 4.2 L of air into your lungs at a temperature of 0°C. If you hold your breath until the temperature of the air in your lungs reaches 37°C, what is the volume of the air in your lungs at that point, assuming the pressure does not change?
A. 4.2 L B. 4.4 L C. 4.6 L D. 4.8 L E. 5.0 L
A monatomic ideal gas undergoes an isothermal expansion at 300 K, as the volume increased from 0.03 m3 to 0.21 m3. The final pressure of the gas is 60 kPA The ideal gas constant is R = 8.314 J/mol ? K
The change in the internal (thermal) energy of the gas is closest to A) 0.00 kJ. B) 12 kJ. C) 25 kJ. D) -12 kJ. E) -25 kJ.
How many possible substates are available in a hydrogen atom where the principal quantum number is 2?
a. 18 c. 36 b. 8 d. 9
In an industrial plant a shell-and-tube heat exchanger is heating pressurized dirty water at the rate of 38 kg/s from 60 to 110°C by means of steam condensing at 115°C on the outside of the tubes. The heat exchanger has 500 steel tubes (ID = 1.6 cm, OD = 2.1 cm) in a tube bundle which is 9-m-long. The water flows through the tubes while the steam condenses in the shell. If it may be assumed that the thermal resistance of the scale on the inside pipe wall is unaltered when the mass rate of flow is increased and that changes in water properties with temperature are negligible, estimate (a) the heat transfer coefficient on the water side and (b) the exit temperature of the dirty water if its mass rate of flow is doubled.
GIVEN
? Shell-and-tube heat exchanger - dirty water in steel tubes, steam condensing in shell
? Water flow rate
( mw ) = 38 kg/s
? Water temperatures
? Tw,in = 60°C
? Tw,out = 110°C
? Steam temperature (Ts) = 115°C
? Number of tubes (N) = 500
? Tube diameters
? Di = 1.6 cm = 0.016 m
? Do = 2.1 cm = 0.021 m
? Tube bundle length (L) = 9 m
FIND
(a) The heat transfer coefficient on the water side
( hi )
(b) The exit temperature of the dirty water (Tw,out) if the mass flow rate
( mw FIND
(a) The heat transfer coefficient on the water side
( ) hi
(b) The exit temperature of the dirty water (Tw,out) if the mass flow rate
( mw ) is double
ASSUMPTIONS
? The thermal resistance of the scale in the pipe is unaltered when the mass flow rate is increased
? Changes in water properties with temperature are negligible
? Two, or a multiple of two, passes
? The dirty water has the same thermal properties as clean water
SKETCH
PROPERTIES AND CONSTANTS
From Appendix 2, Table 13, for water at the average temperature of 85°C
From Appendix 2, Table 10, the thermal conductivity of 1% carbon steel (ks) = 43 W/(m K) (at 20°C)