What is the parallax angle for Proxima Centauri, which is Earth's nearest star at 4.3 ly?
The earth's orbit has a mean radius of 1.5 × 108 km, and 1 ly = 9.46 × 1015 m.
A) 1.2 × 10-7 degrees B) 2.1 × 10-7 degrees
C) 1.2 × 10-14 degrees D) 2.1 × 10-4 degrees
D
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Water at 80°C is flowing through a thin copper tube (15.2-cm-ID) at a velocity of 7.6 m/s. The duct is located in a room at 15°C and the heat transfer coefficient at the outer surface of the duct is 14.1 W/(m2 K). (a) Determine the heat transfer coefficient at the inner surface. (b) Estimate the length of duct in which the water temperature drops 1°C.
GIVEN
• Water flowing through a thin copper tube in a room
• Water temperature (Tb) = 80°C
• Inside diameter of tube (D) = 15.2 cm = 0.152 cm
• Water velocity (V) = 7.6 m/s
• Room air temperature (T?) = 15°C
• Outer surface heat transfer coefficient ( h co ) = 14.1 W/(m2 K)
FIND
(a) The heat transfer coefficient at the inner surface ( h ci )
(b) Length of duct (L) for temperature drop of 1°C
ASSUMPTIONS
• Steady state
• Thermal resistance of the copper tube is negligible
• Fully developed flow
SKETCH
PROPERTIES AND CONSTANTS
for water at 80°C
Density (?) 971.6 kg/m3
Thermal conductivity (k) = 0.673 W/(m K)
Absolute viscosity (?) = 356.7 × 10–6 (Ns)/m2
Prandtl number (Pr) = 2.13
Specific heat (c) = 4194 J/(kg K)
Light of wavelength 550 nm in air is found to travel at 1.96 × 108 m/s in a certain liquid. (c = 3.0 × 108 m/s) (a) What is the index of refraction of this liquid? (b) What is the frequency of the light in air?
What will be an ideal response?
A student kicks a soccer ball in a high arc toward the opponent's goal. At the highest point in its trajectory:
A) both velocity and acceleration of the soccer ball are zero. B) neither the ball's velocity nor its acceleration is zero. C) the ball's acceleration is zero but not its velocity. D) the ball's acceleration points upwards. E) the ball's velocity points downwards.
All Terrestrial planets are separated into layers of different densities
a. True b. False Indicate whether the statement is true or false