Reactance: What is the rms current through a 0.0010-?F capacitor at 1000 Hz and 5.0 V?
A. 5.4 ?A
B. 31 ?A
C. 3.1 mA
D. 10 mA
Answer: B
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A(n) ____________ is a solar-system object that enters Earth's atmosphere and becomes very hot due to friction between the object and Earth's atmosphere and does not survive to reach the surface
a. asteroid b. meteor c. comet d. meteoroid e. planetesimal
What do we think happened to the solar nebula after the planets formed?
a. The gas was all used up in planet formation. b. The rest of the gas gradually drifted away. c. The solar wind helped blow the gas away. d. The gas is still here; we just can’t see it.
Mild steel nails were driven through a solid wood wall consisting of two layers, each 2.5- cm-thick, for reinforcement. If the total cross-sectional area of the nails is 0.5% of the wall area, determine the unit thermal conductance of the composite wall and the per cent of the total heat flow that passes through the nails when the temperature difference across the wall is 25°C. Neglect contact resistance between the wood layers.
GIVEN
• Wood wall
• Two layers 0.025-m-thick each
• Nail cross sectional area of nails = 0.5% of wall area
• Temperature difference (?T) = 25°C
FIND
(a) The unit thermal conductance (k/L) of the wall (b) Percent of total heat flow that passes through the wall
ASSUMPTIONS
• One dimensional heat transfer through the wall
• Steady state prevails
• Contact resistance between the wall layers is negligible
SKETCH
PROPERTIES AND CONSTANTS
? Wood (Pine) (kw) = 0.15 W/(m K)
? Mild steel (1% C) (ks) = 43 W/(m K)
A race car traveling at 100 m/s enters an unbanked turn of 400 m radius. The coefficient of (static) friction between the tires and the track is 1.1 . The track has both an inner and an outer wall. Which statement is correct?
a. The race car will crash into the outer wall. b. The race car will crash into the inner wall. c. The car will stay in the center of the track. d. The car will stay in the center of the track if the driver speeds up. e. The car would stay in the center of the track if the radius were reduced to 200 m.