A 50-cm3 block of wood is floating on water, and a 50-cm3 chunk of iron is totally submerged in the water. On which one the water exerts the greater buoyant force?
A) on the wood
B) on the iron
C) The same buoyant force is exerted on both.
D) It cannot be determined without knowing their densities.
B
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In the late 1800s, Kelvin and Helmholtz suggested that the Sun stayed hot because of gravitational contraction. What was the major drawback to this idea?
A) It predicted that the Sun could shine for about 25 million years, but geologists had already found that Earth is much older than this. B) It predicted that the Sun would shrink noticeably as we watched it, but the Sun appears to be stable in size. C) It is physically impossible to generate heat simply by making a star shrink in size. D) It predicted that Earth would also shrink in size with time, which would make it impossible to have stable geology on our planet.
What is the inductance of a series RL circuit in which R = 1.0 K? if the current increases to one-third of its final value in 30 ?s?
A. 74 mH B. 99 mH C. 49 mH D. 62 mH E. none of the above
The small circles in the diagram below represent the positions along the x axis of a body at equal time intervals. Assume the body moves in a straight line
This diagram is most likely to describe
a.
a swimmer swimming laps.
b.
an exercise on a rowing machine.
c.
a person on a treadmill.
d.
a tennis ball during a volley.
e.
a runner who tripped, fell, rose, and continued racing.
In a lead-shot tower, spherical 0.95-cm-diameter BB shots are formed by drops of molten lead which solidify as they descend in cooler air. At the terminal velocity, i.e., when the drag equals the gravitational force, estimate the total heat transfer coefficient if the lead surface is at 171°C, the surface of the lead has an emissivity of 0.63, and the air temperature is 16°C. Assume CD = 0.75 for the first trial calculation.
GIVEN
• Spherical lead-shot falling through the air at terminal velocity
• Shot diameter (D) = 0.95 cm = 0.0095 m
• Lead surface temperature (Ts) = 171°C = 494 K
• Lead surface emissivity (?) = 0.63
• Air temperature (T?) = 16°C 289 K
• Assume CD = 0.75 for the first trial calculation FIND
• The total average heat transfer coefficient (htotal). ASSUMPTIONS
• The surroundings act as a black body enclosure at T?
SKETCH
