Your motorboat can move at 30 km/h in still water. How much time will it take you to move 12 km upstream, in a river flowing at 6 km/h?
A) 22 min
B) 26 min
C) 20 min
D) 30 min
E) 24 min
D
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Wearing layers of clothing in cold weather is often recommended because dead-air spaces between the layers keep the body warm. The explanation for this is that the heat loss from the body is less. Compare the rate of heat loss for single 2 cm thick layer of wool [k = 0.04 W/(m K)] with three 0.67 cm layers separated by 1.5 mm air gaps. The thermal conductivity of air is 0.024 W/(m K).
GIVEN
• Wool insulation
• Thermal conductivities
? Wool (kw) = 0.04 W/(m K
? air (ka) = 0.024 W/(m K)
FIND
• Compare the rate of heat loss for a single 2 cm thick layer of wool to that of three 0.67 cm layers separated by 1.5 mm layers of air gaps.
ASSUMPTIONS
• Heat transfer can be approximated as one dimensional, steady state conduction
SKETCH
What is the exosphere?
A) the lowest layer in the atmosphere B) the part of the atmosphere that absorbs optical light C) the part of the atmosphere that absorbs ultraviolet D) the part of the atmosphere that absorbs X-rays E) the highest layer in the atmosphere
A uniform rod (mass = 2.0 kg, length = 0.60 m) is free to rotate about a frictionless pivot at one end. The rod is released from rest in the horizontal position. What is the magnitude of the angular acceleration of the rod at the instant it is 60° below the horizontal?
A. 15 rad/s2 B. 12 rad/s2 C. 18 rad/s2 D. 29 rad/s2 E. 23 rad/s2
Internal human body temperature is often stated to be normal at 98.6°F. What is this temperature on the Celsius scale?
A) 120°C B) 145°C C) 37.0°C D) 72.6°C E) 22.8°C