A negatively-charged balloon touching a wooden wall
A) pulls positive charge on the wall surface toward it.
B) pushes negative charge in the wall away from it.
C) polarizes molecules in the wall.
D) all of the above
E) none of the above
Answer: D
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The force that causes Earth to orbit the Sun is due to gravity, while the force needed to keep Earth moving as it circles the Sun is
A) inertia. B) due to gravity. C) due to both inertia and gravity. D) no force at all.
Find the net work done by friction on the body of a snake slithering in a complete circle of 3.93 m radius. The coefficient of friction between the ground and the snake is 0.25, and the snake's weight is
A) -330 J B) 0 J C) -3300 J D) -670 J
The inside surface of a 1-m-long vertical 5-cm-ID tube is maintained at 120°C. For saturated steam at 350 kPa condensing inside, estimate the average heat transfer coefficient and the condensation rate, assuming the steam velocity is small.
GIVEN
? Steam condensing inside a vertical tube
? Tube length (L) = 1 m
? Tube inside diameter (D) = 5 cm = 0.05 m
? Tube surface temperature (Ts) = 120°C
? Steam pressure (p) = 350 kPa
FIND
? The average heat transfer coefficient (hc)
ASSUMPTIONS
? Steady state
? The steam velocity is small
? Film condensation occurs
SKETCH
PROPERTIES AND CONSTANTS
From Appendix 2, Table 13, for saturated water at 350 kPa
If there is no dark matter in the Milky Way Galaxy, what is the best alternative explanation for the observations?
A) We are not measuring the orbital velocities of atomic clouds and stars properly. B) We are not measuring the distances to atomic clouds and stars properly. C) We are not attributing enough mass to the visible or "bright" matter. D) We are not observing all the visible or "bright" matter in the galaxy. E) Our understanding of gravity is not correct for galaxy-size scales.