Five motion diagrams in which points represent the positions of an object at equal time intervals are shown below. Which statement is correct?
?
A. A has the greatest speed and the greatest acceleration.
B. C has decreasing speed.
C. D slows down and then speeds up.
D. D speeds up and then slows down.
E. E has a greater speed than A.
Answer: D
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Atmospheric air at 10°C enters a 2 m long smooth rectangular duct with a 7.5 cm x 15 cm cross-section. The mass flow rate of the air is 0.1 kg/s. If the sides are at 150°C, estimate (a) the heat transfer coefficient, (b) the air outlet temperature, (c) the rate of heat transfer, and (d) the pressure drop.
GIVEN
Atmospheric air flow through a rectangular duct
Inlet bulk temperature (Tb,in) = 10°C
Duct length (L) = 2 m
Cross-section = 7.5 cm x 15 cm = 0.075 m ? 0.15 m
Mass flow rate (m) = 0.1 kg/s
Duct surface temperature (Ts) = 150°C
FIND
(a) The heat transfer coefficient ch
(b) The air outlet temperature (Tb,out)
(c) The rate of heat transfer (q)
(d) The pressure drop (?p)
ASSUMPTIONS
Steady state
The duct is smooth
SKETCH
for dry air at the inlet bulk temperature of 20°C
Thermal conductivity (k) = 0.0251 W/(m K)
Absolute viscosity (?) = 18,240 × 10–6 (Ns)/m2
Prandtl number (Pr) = 0.71
Specific heat (c) = 1012 J/(kg K)
Tides are influenced by
a. the Moon. b. the Sun. c. the uneven surface of the Earth. d. all of the above. e. none of the above.
Two particles, each having a mass of 3.0 ?g and having equal but opposite charges of magnitude of 6.0 nC, are released simultaneously from rest when they are a very large distance apart. What distance separates the two at the instant when each has a speed of 5.0 m/s?
A. 4.3 mm B. 8.6 mm C. 7.3 mm D. 5.6 mm E. 2.2 mm
The huge sheet of galaxies that spans 70 × 200 Mpc is called the ________
Fill in the blank(s) with correct word