The power rating of a 400-? resistor is 0.800 W
(a) What is the maximum safe voltage across this resistor?
(b) What is the maximum current the resistor can safely draw?
(a) 17.9 V (b) 44.7 mA
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A fancy sports car moves past an observer on a corner at a speed of 0.600 c. When the observer indicates a one-second interval has passed, what time interval will be shown on the driver's watch?
a. 1.67 s b. 0.800 s c. 1.25 s d. 0.600 s e. 1.00 s
Carbon-fiber reinforced epoxy is being used as the outer surface material in high-performance aircraft where the surface temperatures are elevated because of the friction with air. The maximum-use temperature for epoxy resin is approximately 260°C. A composite sheet is produced from 75 vol % carbon fiber and 25 vol % epoxy resin. Assume that the epoxy and carbon are stress free at room temperature, and the composite is heated from room temperature (22°C) to 260°C during service. The elastic modulus of the carbon fiber is 380 GPa, the ultimate tensile strength is 2.4 GPa, and the axial thermal expansion coefficient is –0.7×10-6 K-1 . The elastic modulus of the epoxy resin is 4 GPa, the ultimate tensile strength is 0.07 GPa, and the thermal expansion coefficient is 60×10-6 K-1 .
(a) Calculate the thermal stresses, both the magnitude and sign, in the epoxy matrix and in the carbon fibers at 260°C. Assume that each material is elastic at all temperatures, and that there is good interface bonding. (b) Calculate the composite strain in heating from 22°C to 260°C. (c) Is there any component of this design that might cause a problem? Comment on the results in comparison to the data provided. If data is not available on these components, justify your evaluation of this design based upon your knowledge of these materials.
A railroad freight car, mass 15,000 kg, is allowed to coast along a level track at a speed of 2.0 m/s. It collides and couples with a 60,000-kg loaded second car, initially at rest and with brakes released. What percentage of the initial kinetic energy of the 15,000-kg car is preserved in the two-coupled cars after collision?
a. 20% c. 86% b. 23% d. 100%
A meteoroid, meteor, and meteorite could come from the same celestial body
a. True b. False Indicate whether the statement is true or false