After nuclear reactions in the big bang had ended, about 25% of the mass of the Universe was in the form of helium nuclei.?

Two 4.0-? resistors are connected in parallel, and this combination is connected in series with 3.0 ?. What is the equivalent resistance of this system?

A) 1.2 ? B) 5.0 ? C) 7.0 ? D) 11 ?

In its lowest quantum state, a diatomic quantum mechanical rotator has a rotational energy of

A) zero. B) 2h/?I. C) h/2?I. D) h/?I. E) none of the given answers

Cooled air is flowing through a long sheet metal air conditioning duct, 0.2 m high and 0.3 m wide. If the duct temperature is 10°C and passes through a crawl space under a house at 30°C, estimate

(a) The heat transfer rate to the cooled air per meter length of duct.
(b) The additional air conditioning load if the duct is 20-m-long.
(c) Discuss qualitatively the energy conservation if the duct were insulated with glass
wool.
GIVEN
• An air conditioning duct in a crawl space
• Duct height (H) = 0.2 m
• Duct width (w) = 0.3 m
• Duct temperature (Ts) = 10°C
• Ambient temperature (T?) = 30°C
FIND
(a) The heat transfer rate per meter length (qc/L) to the cooled air in the duct
(b) The additional air conditioning load (q20) if the duct length (L) = 20 m
(c) Discuss qualitatively the energy conservation if the duct were insulated with glass wool
ASSUMPTIONS
• Ambient air is still
• Duct temperature is constant and uniform
• Radiation is negligible
• Edge effects are negligible
• No condensation on the duct surface
SKETCH

PROPERTIES AND CONSTANTS
for dry air at the mean temperature of 20°C
Thermal expansion coefficient (?) = 0.00341 1/K
Thermal conductivity (k) = 0.0251 W/(m K)
Kinematic viscosity (?) = 15.7 × 10–6 m2/s
Prandtl number (Pr) = 0.71

Stratification, or ______________, is the layering that develops at the time sediments are deposited

Fill in the blank(s) with correct word