Sorted spectral data and designed the stellar spectral types

If a car engine has a thermal efficiency of 50% and it does 500 J of work in one cycle, how much energy input does it require each cycle?

1.250 J 2.500 J 3.750 J 4.1000 J

Four identical particles (mass of each = 0.40 kg) are placed at the vertices of a rectangle (2.0 m × 3.0 m) and held in those positions by four light rods which form the sides of the rectangle. What is the rotational inertia of this rigid body about an axis that passes through the mid-points of the longer sides and is parallel to the shorter sides?

a. 2.7 kg/m2 b. 3.6 kg/m2 c. 3.1 kg/m2 d. 4.1 kg/m2 e. 1.6 kg/m2

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)

Given that white dwarf supernovae are such good standard candles, why don't we use them to measure the distance to all galaxies?

A) They are rare events, so we have observed them in only a tiny fraction of all galaxies. B) We cannot see them beyond a distance of about 100 million light-years. C) They can occur only in spiral galaxies, not elliptical galaxies. D) We would, but we don't have enough telescopes.