A ventilation fan with a moment of inertia of 0.040 kg·m2 has a net torque of 0.160 N·m applied to it. What angular acceleration does it experience?
a. 0.0064 rad/s2 b. 4.0 rad/s2
c. 0.25 rad/s2 d. 0.40 rad/s2
e. 0.20 rad/s2
b
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Coastal upwelling helps to decrease the surface water temperature off the central California coast.
Answer the following statement(s) true (T) or false (F)
2.0 L of a ideal nitrogen gas (N2 ) are at 0.00°C and 1.0 atm. The ideal gas constant is R = 8.314 J/mol • K = 0.0821 L ? atm/mol ? K, Avogadro's number is 6.022 × 1023 molecules/mol,
and the ATOMIC mass of nitrogen is 14 g/mol. (a) Determine the number of moles of N2. (b) How many molecules of N2 are present? (c) What is the mass of this gas?
In a uniformly expanding universe, which statement best describes the situation as viewed from an observer in Galaxy C (not the Milky Way Galaxy)?
A) Galaxy C observer sees some galaxies moving away, some moving towards itself. B) Galaxy C observer sees all galaxies moving away from the Milky Way Galaxy. C) Galaxy C observer sees all other galaxies moving away from itself.
The heat loss from uninsulated hot water pipes installed in homes can be considerable and hence increases the overall energy cost of the home. Consider a 5-m-long section of such a pipe that has an outer diameter of 1.7 cm and a surface temperature of 75°C. If the room air temperature is 20°C, calculate the natural convection heat loss from the pipe section. If the radiation heat losses are to be included as well, determine its contribution as a percentage of the total pipe heat transfer rate; assume that the outer pipe surface has an emissivity of 0.7.
GIVEN
• Uninsulated hot water pipe dissipating heat to surrounding
• Emissivity (?) = 0.7
• Diameter of cylinder (D) = 1.7 cm= 0.017 m
• Surface temperature (Ts) = 75°C= 348 K
• Ambient air temperature (T?) = 20°C= 293 K
• Length of the cylinder (L)= 5 m
FIND
(a) Natural convection heat loss from pipe section.
(b) Contribution of radiation as percentage of
total pipe heat transfer rate.
SKETCH
ASSUMPTIONS
• Air is still
• Surface temperature is uniform and constant
PROPERTIES AND CONSTANTS
for dry air at the mean temperature of 47.5°C
Thermal expansion coefficient (?) = 0.00312 1/K
Thermal conductivity (k) = 0.02695 W/(m K)
Kinematic viscosity (?) = 18.27 × 10–6 m2/s
Prandtl number (Pr) = 0.71