If a wave pulse is reflected from a free boundary, which of the following choices best describes what happens to the reflected pulse?
a. becomes inverted
c. halved in amplitude
b. remains upright
d. doubled in amplitude
B
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To decrease the size of personal computer mother boards, designers have turned to a more compact method of mounting memory chips on the board. The single in-line memory modules, as they are called, essentially mount the chips on their edges so that their thin dimension is horizontal, as shown in the sketch below. For safe operation (so that the VLSI microchips do not “burn out”), their maximum temperature always has to be <=75°C under all operating conditions. Assuming that the memory board, housing the chip modules, is also at the same temperature, determine the maximum power that is dissipated from the chips if the board is cooled by air at 20°C. The air flows perpendicular to the board face, as shown in the figure, with a velocity of 10 m/s. Consider the heat loss from both the
front face and back face of the memory-modules board. Is it beneficial (dissipate more heat) if the board was aligned parallel to the air flow? To model the board, in both cases, consider an equivalent “square” of the same rectangular face area and determine the appropriate length scale.
GIVEN
• Computer memory chip in an air stream as shown above
• Chip temperature (Ts) = 90°C
• Air temperature (T?) = 20°C
• Air velocity (U?) = 10 m/s FIND
• The maximum power dissipation ( Q G)
ASSUMPTIONS
• Radiative heat transfer is negligible
• Use for a non-square surface will not introduce significant error
• Heat transfer from all four edges of the chip is negligible
An ideal spring has a spring constant (force constant) of 60 N/m. How much energy does it store when it is stretched by 1.0 cm?
A) 0.30 J B) 60 J C) 0.0030 J D) 600 J
At a distance of 4.3 cm from the center of a very long uniformly charged wire, the electric field has magnitude 2000 N/C and is directed toward the wire
What is the charge on a 1.0 cm length of wire near the center? (?0 = 8.85 × 10-12 C2/N ? m2) A) -0.056 nC B) -0.044 nC C) -0.048 nC D) -0.052 nC
Which is not a general classification of mountains?
a. Fault-block b. Fold c. Continental d. Volcanic