In a contest, two tractors pull two identical blocks of stone the same distance over identical surfaces. However, block A is moving twice as fast as block B when it crosses the finish line. Which statement is correct?
a. Block A has twice as much kinetic energy as block B.
b. Block B has lost twice as much kinetic energy to friction as block A.
c. Block B has lost twice as much kinetic energy as block A.
d. Both blocks have had equal losses of energy to friction.
e. No energy is lost to friction because the ground has no displacement.
d
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A 3 solar mass main sequence star is at the same distance as a 0.4 solar mass main sequence star. Which star appears brighter?
A. depends on the phase of the Moon B. the 0.4 solar mass main sequence star C. stars are approximately the same brightness D. the 3 solar mass main sequence star E. cannot tell with the information given
Jupiter's interior is mostly liquid helium
a. True b. False Indicate whether the statement is true or false
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