For which value of ? is the range of a projectile fired from ground level a maximum?
A) 30° above the horizontal
B) 45° above the horizontal
C) 55° above the horizontal
D) 60° above the horizontal
E) 90° above the horizontal
B
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The star Wolf 1061 has a parallax of 2.34 arcseconds, while the star Ross 652 has a parallax of 1.70 arcseconds. What can you correctly conclude?
A) Both stars are outside the Milky Way galaxy. B) Wolf 1061 must have a larger proper motion than Ross 652. C) Ross 652 must have a larger proper motion than Wolf 1061. D) Ross 652 is closer to Earth than Wolf 1061. E) Wolf 1061 is closer to Earth than Ross 652.
Massive-star supernovae and white-dwarf supernovae work equally well as standard candles for measuring cosmic distances
Indicate whether the statement is true or false
A homeowner wants to replace an electric hot-water heater. There are two models in the store. The inexpensive model costs $280 and has no insulation between the inner and outer walls. Due to natural convection, the space between the inner and outer walls has an effective conductivity of 3 times that of air. The more expensive model costs $310 and has fiberglass insulation in the gap between the walls. Both models are 3.0 m tall and have a cylindrical shape with an inner wall diameter of 0.60 m and a 5 cm gap. The surrounding air is at 25°C, and the convective heat transfer coefficient on the outside is 15 W/(m2 K). The hot water inside the tank results in an inside wall temperature of 60°C. If energy costs 6 cents per kilowatt-hour, estimate how long it will take to pay back the extra
investment in the more expensive hot-water heater. State your assumptions.
GIVEN
FIND
- The time it will take to pay back the extra investment in the more expensive hot-water heater
ASSUMPTIONS
- Since the diameter is large compared to the wall thickness, one-dimensional heat transfer is
assumed
- To simplify the analysis, we will assume there is no water drawn from the heater, therefore the
inside wall is always at 60°C
- Steady state conditions prevail
SKETCH
PROPERTIES AND CONSTANTS
fiberglass (ki) = 0.035 W/(m K) at 20°C
dry air (ka) = 0.0279 W/(m K) at 60°C
The third step in the precipitation-hardening process is to _________ the alloy to form the precipitate.
Fill in the blank(s) with the appropriate word(s).