A uniform solid sphere of mass M and radius R rotates with an angular speed ? about an axis through its center
A uniform solid cylinder of mass M, radius R, and length 2R rotates through an axis running through the central axis of the cylinder. What must be the angular speed of the cylinder so it will have the same rotational kinetic energy as the sphere?
A) 2?/5
B) ?
C) 4?/5
D) 2?/
E) ?/
Answer: D
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In a shell-and-tube heat exchanger with h i= h o= 5600 W/(m2 K) and negligible wall resistance, by what per cent would the overall heat transfer coefficient (based on the outside area) change if the number of tubes was doubled? The tubes have an outside diameter of 2.5 cm and a tube wall thickness of 2 mm. Assume that the flow rates of the fluids are constant, the effect of temperature on fluid properties is negligible, and the total cross sectional area of the tubes is small compared to the flow area of the shell.
GIVEN
• Shell and tube heat exchanger
• Heat transfer coefficients: h i= h o= 5600 W/(m2 K)
• Negligible wall resistance
• Tube outside diameter (Do) = 2.5 cm = 0.025 m
• Tube wall thickness (t) = 2 mm = 0.002 m
FIND
• The per cent change in the overall heat transfer coefficient if the number of tubes is doubled
ASSUMPTIONS
• Flow rates of the fluids are constant
• The effect of temperature of fluid properties is negligible
• The fluid flow is turbulent in the tubes (this is consistent with the high heat transfer coefficients)
SKETCH
Length Contraction: The figure shows a right-angled construction frame ABC. When measured at rest, it has dimensions as follows: AB = 26.0 m, AC = 10.0 m, and BC = 24.0 m. This frame is now given a new velocity of 0.760c, relative to Earth, in a direction parallel to AC. How long is part AC of this frame with the new velocity as measured by Earth-based engineers?
A. 6.50 m B. 25.4 m C. 24.3 m D. 23.7 m E. 24.9 m
Most of the mass of the Milky Way is in the form of
A) stars B) gas clouds C) black holes D) dark matter
Automobile air bags reduce what during a collision?
A) speed of the automobile B) the forces exerted upon the passenger C) the kinetic energy transferred to the passenger D) the impulse exerted upon the passenger