In essence, the Kepler mission searched for extrasolar planets by ________
A) observing a star carefully enough to notice that it is experiencing a gravitational tug caused by an unseen planet
B) identifying spectral lines that look like what we expect to see from a planet rather than a star
C) monitoring stars for slight dimming that might occur as unseen planets pass in front of them
D) obtaining high-resolution photographs of other star systems
C
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To measure the mass flow rate of a fluid in a laminar flow through a circular pipe, a hot wire type velocity meter is placed in the center of the pipe. Assuming that the measuring station is far from the entrance of the pipe, the velocity distribution is parabolic where Umax is the centerline velocity (r = 0), r is the radial distance from the pipe centerline, D is the pipe diameter.
(a) Derive an expression for the average fluid velocity at the cross-section in terms of
Umax and D.
(b) Obtain an expression for the mass flow rate.
(c) If the fluid is mercury at 30°C, D = 10 cm, and the measured value of Umax is 0.2
cm/s, calculate the mass flow rate from the measurement.
GIVEN
• Fully developed flow of mercury through a circular pipe
• Parabolic velocity distribution: u(r)/Umax = 1 – (2r/D)2
• Mercury temperature (T) = 30°C
• Pipe diameter (D) = 10 cm = 0.1 m
• Measured center velocity (Umax) = 0.2 cm/s = 0.002 m/s
FIND (a) An expression for the average fluid velocity (u )
(b) An expression for the mass flow rate (m )
c) The value of the mass flow rate (m )
SKETCH
When we say that Jupiter is at opposition we mean that it
A) is behind the Sun as seen from Earth, so that it appears very close to the Sun in our sky. B) is at its greatest western elongation. C) it is at the point in its orbit where it is farthest from the Sun. D) appears on the opposite side of the sky from the Sun, so that it is on our meridian at midnight.
Which star shows the least motion in the northern sky over the course of an hour?
What will be an ideal response?
Suppose the entire solar nebula had cooled to a very low temperature before the solar wind cleared it away. Do you think Earth would be the same? Why or why not?
What will be an ideal response?