Suppose you are using the Doppler technique to look for planets around another star. What must you do?
A) Compare many spectra of an orbiting planet taken over a period of many months or years.
B) Compare the brightness of the star over a period of many months or years.
C) Carefully examine a single spectrum of an orbiting planet.
D) Compare many spectra of the star taken over a period of many months or years.
D
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Graphical Analysis: The graph in the figure shows the position of a particle as it travels along the x-axis. 
At what value of t is the speed of the particle equal to 0 m/s?
A. 0 s B. 1 s C. 2 s D. 3 s E. 4 s
A solar thermal central receiver generates heat by focusing sunlight with a field of mirrors on a bank of tubes through which a coolant flows. Solar energy absorbed by the tubes is transferred to the coolant which can then deliver useful heat to a load. Consider a receiver fabricated from multiple horizontal tubes in parallel. Each tube is 1-cm-ID and 1-m-long. The coolant is molten salt which enters the tubes at 370°C. Under start-up conditions, the salt flow is 10 gm/s in each tube and the net solar flux absorbed by the tubes is 104 W/m2. The tube wall material will tolerate temperatures up to 600°C. Will the tubes survive start-up? What is the salt outlet temperature?
GIVEN
• Molten salt flowing through a horizontal tube that is absorbing solar energy
• Tube inside diameter (D) = 1 cm = 0.01 m
• Tube length (L) = 1 m
• Entering salt temperature (Tb,in) = 370°C
• Start-up mass flow rate (m) = 10 gm/s = 0.01 kg/s
• Net solar energy absorbed by the tube (qs) = 104 W/m2
• Maximum tube wall temperature (Ts) = 600°C
FIND
(a) Salt outlet temperature (Tb,out)
(b) Will the tubes survive start-up?
SKETCH
PROPERTIES AND CONSTANTS
for molten salt at 370°C
Specific heat (c) = 1629 J/(kg K)
How much energy is dissipated as heat during a two-minute time interval by a 1.5-k? resistor which has a constant 20-V potential difference across its leads?
a. 58 J b. 46 J c. 32 J d. 72 J e. 16 J
A proton's rest mass is 1.67 × 10?27 kg. Calculate its kinetic energy when it is accelerated to a speed of 0.80c.
A. 1.0 × 10?10 J B. 1.5 × 10?10 J C. ?2.0 × 10?10 J D. 2.5 × 10?10 J E. 7.5 × 10?10 J