Why did Galileo's observations of moons orbiting Jupiter disagree with geocentric model of the universe of his time?
a. The moons moved in non-circular orbits about Jupiter.
b. The moons did not appear to orbit the Sun.
c. The moons did not appear to orbit the Earth.
d. The moons appeared to be too small, and therefore too far away, to be considered part of the solar system.
C
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if the extrusion cross-section is elliptical with the major axis normal to the air flow and same mass per unit length. The major axis of the elliptical cross-section is 5.46 cm and its perimeter is 12.8 cm
GIVEN
• A long elliptical copper extrusion in an air stream
• Initial temperature (To) = 400°C
• Air Temperature (T?) = 50°C
• Air velocity (V?) = 10 m/s
• Surface emissivity (?) = 0.9
• Elliptical cross-section with major axis normal to the air flow
• Length of the major axis of the ellipse (D) = 5.46 cm = 0.0546 m
• Perimeter of ellipse (P) = 12.8 cm = 0.128 m
• Same mass per unit length as Problem 6.9
FIND
• The time (t) required for the center of the copper to cool to 100°C
ASSUMPTIONS
• Air flow is perpendicular to the axis of the extrusion
• Variation of the copper properties with temperature is negligible
SKETCH
PROPERTIES AND CONSTANTS
the initial and final film temperature of 150°C
Thermal conductivity (ka) = 0.0339 W/(m K) Kinematic viscosity (?) = 29.6 × 10–69 m2/s Prandtl number (Pr) = 0.71
Thermal conductivity (k) = 386 W/(m K) at 250°C Density (?) = 8933 kg/m3 at 20°C Specific heat (c) = 383 J/(kg K) at 20°C
The kinetic coefficient of friction is usually larger than the static coefficient of friction
Indicate whether the statement is true or false
The bob of a conical pendulum swings in a
A) to-and-fro path. B) circular path. C) chaotic path.
Why is the cosmic microwave background (CMB) so cold if the early universe was so hot?
a. Enough time has passed for matter in the universe to release enough heat to cool down. b. The CMB constantly interacts with atoms, which effectively cool down the photons. c. The expansion of the universe has redshifted those photons to an effectively cooler temperature. d. Misleading; The Big Bang was initially hot but the CMB was released from cold material much later on.