What is happening when two plates are smashing into one another?
A. Precession causes mountains to be built up; earthquakes and volcanoes may also occur.
B. Subduction causes mountains to be built up; earthquakes and volcanoes may also occur.
C. Rifting causes mountains to be built up; earthquakes and volcanoes may also occur.
D. nothing
Answer: B
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Viscosity: Glycerin, with a viscosity of 1.5 N ? s/m2, is flowing with an average speed of 1.2 m/s through a tube that has a radius of 5.0 mm and is 25 cm long. What is the drop in pressure over the length of this pipe?
A. 140 kPa B. 46 kPa C. 72 kPa D. 76 kPa E. 130 kPa
A uniformly charged rod (length = 2.0 m, charge per unit length = 5.0 nC/m) is bent to form one quadrant of a circle. What is the magnitude of the electric field at the center of the circle?
a. 62 N/C b. 56 N/C c. 50 N/C d. 44 N/C e. 25 N/C
Energy in Capacitors: An ideal parallel-plate capacitor consists of two parallel plates of area A separated by a distance d. This capacitor is connected to a battery that maintains a constant potential difference across the plates. If the separation between the plates is now doubled, the amount of electrical energy stored on the capacitor will
A. double. B. quadruple. C. be cut in half. D. be cut in fourth. E. not change.
In order to prevent frostbite to skiers on chair lifts, the weather report at most ski areas gives both an air temperature and the wind chill temperature. The air temperature is measured with a thermometer that is not affected by the wind. However, the rate of heat loss from the skier increases with wind velocity, and the wind-chill temperature is the temperature that would result in the same rate of heat loss in still air as occurs at the measured air temperature with the existing wind. Suppose that the inner temperature of a 3-mm-thick layer of skin with a thermal conductivity of 0.35 W/(m K) is 35°C and the ambient air temperature is –20°C. Under calm ambient conditions the heat transfer coefficient at the outer skin surface is about 20 W/(m2 K) but in a 40 mph wind it increases to
75 W/(m2 K). (a) If frostbite can occur when the skin temperature drops to about 10°C, would you advise the skier to wear a face mask? (b) What is the skin temperature drop due to wind?
GIVEN
• Skier’s skin exposed to cold air
• Skin thickness (L) = 3 mm = 0.003 m
• Inner surface temperature of skin (Tsi) = 35°C
• Thermal conductivity of skin (k) = 0.35 W/(m K)
• Ambient air temperature (T?) = –20°C
• Convective heat transfer coefficients
? Still air (hc0) = 20 W/(m2 K)
? 40 mph air (hc40) = 75 W/(m2 K)
• Frostbite occurs at an outer skin surface temperature (Tso) = 10°C FIND
(a) Will frostbite occur under still or 40 mph wind conditions? (b) Skin temperature drop due to wind chill.
ASSUMPTIONS
• Steady state conditions prevail
• One dimensional conduction occurs through the skin
• Radiative loss (or gain from sunshine) is negligible
SKETCH
