A 25-g traffic light hangs midway on a cable between two poles 40 meters apart. If the sag in the cable is 0.40 meters, what is the tension in each side of the cable?
a. 12,200 N
c. 4900 N
b. 9800 N
d. 6100 N
D
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A ball rolling down an incline has its maximum kinetic energy at
A) the top. B) half-way down. C) three-quarters of the way down. D) the bottom.
Which of the following wavelengths could NOT be present as a standing wave in a 2-m-long organ pipe open at both ends?
a. 4 m b. 2 m c. 1 m d. 0.89 m e. 0.5 m
One of the most unexpected aspects of Mars' atmosphere is:
A) that it is 95% carbon dioxide. B) that its troposphere changes altitude. C) that it is cloudless. D) that it contains water vapor clouds. E) that it has such a low density.
A stainless steel pin fin 5-cm-long, 6-mm-OD, extends from a flat plate into a 175 m/s air stream as shown in the sketch. Estimate (a) the average heat transfer coefficient between air and the fin. (b) the temperature at the end of the fin. (c) the rate of heat flow from the fin with glycerol at 20°C flowing over the fin at 2 m/s. The plate temperature is 50°C.
GIVEN
• A stainless steel pin fin in an air stream
• Pin length (L) = 5 cm = 0.05 m
• Pin diameter (D) = 6 mm = 0.006 m
• Glycerol velocity (U?) = 2 m/s
• Glycerol temperature (T?) = 20°C
• Plate temperature (Tp) = 50°C FIND
(a) The average heat transfer coefficient ( h c) (b) The temperature of the end of the fin (TL) (c) The rate of heat flow from the fin (qf) ASSUMPTIONS
• Steady state
• Turbulence in the glycerol approaching the fin is low
• Radiative heat transfer is negligible
• Steel is type 304
• Steel properties are uniform
• Variation of the thermal properties of glycerol and steel with temperature is negligible
PROPERTIES AND CONSTANTS
Thermal conductivity (k) = 0.285 W/(m K) Kinematic viscosity (?) = 1175 × 10–6 m2/s Prandtl number (Pr) = 12,609 for type 304 stainless steel ks = 14.4 W/(m K) at 20°C
