What is the optic axis of a concave mirror?
a. The line along which light reflects from the mirror.
b. The line from one edge of the mirror to the other, marking off the mirror's arc.
c. Any line that is perpendicular to the mirror surface.
d. The line that passes through the center of the mirror and the center of the sphere that the mirror surface is part of.
e. The line perpendicular to the plane of the mirror.
d
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Water at 80°C is flowing through a thin copper tube (15.2-cm-ID) at a velocity of 7.6 m/s. The duct is located in a room at 15°C and the heat transfer coefficient at the outer surface of the duct is 14.1 W/(m2 K). (a) Determine the heat transfer coefficient at the inner surface. (b) Estimate the length of duct in which the water temperature drops 1°C.
GIVEN
• Water flowing through a thin copper tube in a room
• Water temperature (Tb) = 80°C
• Inside diameter of tube (D) = 15.2 cm = 0.152 cm
• Water velocity (V) = 7.6 m/s
• Room air temperature (T?) = 15°C
• Outer surface heat transfer coefficient ( h co ) = 14.1 W/(m2 K)
FIND
(a) The heat transfer coefficient at the inner surface ( h ci )
(b) Length of duct (L) for temperature drop of 1°C
ASSUMPTIONS
• Steady state
• Thermal resistance of the copper tube is negligible
• Fully developed flow
SKETCH
PROPERTIES AND CONSTANTS
for water at 80°C
Density (?) 971.6 kg/m3
Thermal conductivity (k) = 0.673 W/(m K)
Absolute viscosity (?) = 356.7 × 10–6 (Ns)/m2
Prandtl number (Pr) = 2.13
Specific heat (c) = 4194 J/(kg K)
An ideal spring with a spring constant (force constant) of 22N/m is stretched from equilibrium to 2.9 m. How much work is done in the process?
A) 186 J B) 47 J C) 121 J D) 93 J
When an acid reacts with a carbonate or hydrogen carbonate, the products are water, ______________, and a salt
Fill in the blank(s) with correct word
A 10-pound sack of potatoes falls from an airplane. As the velocity of the falling sack increases, so does the air resistance on it. When the air resistance equals 10 pounds, the acceleration of the sack will be
A. zero. B. 9.8 m/s. C. 9.8 m/s2. D. 100 ft/s2.