What is the product of 11.24 and 1.95 written with the correct number of significant figures?
A) 22 B) 21.9 C) 21.92 D) 21.918 E) 21.9180
B
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An SBc galaxy in the Hubble classification system would have...
A. a barred spiral shape with tight arms. B. a spiral shape with tight arms. C. a barred spiral shape with loose arms. D. an elliptical shape with a medium elongation.
Line waves with wavelength ? going through a slit with width a will be diffracted into circular waves with approximately equal amplitude in all forward directions
A. Always B. Never C. Only if ? >> a D. Only if a >> ? E. Only if a = ?
Nearsighted people wear glasses with
lenses that are designed to a) make the image larger. b) improve the focus of the image. c) make the image smaller. d) make the image brighter.
Heat is transferred at a rate of 0.1 kW through glass wool insulation (density = 100 kg/m3 ) with a 5 cm thickness and 2 m2 area. If the hot surface is at 70°C, determine the temperature of the cooler surface.
GIVEN
• Glass wool insulation with a density (?) = 100 kg/m3
• Thickness (L) = 5 cm = 0.05 m
• Area (A) = 2 m2
• Temperature of the hot surface (Th) = 70°C
• Rate of heat transfer (qk) = 0.1 kW = 100 W
FIND
• The temperature of the cooler surface (Tc)
ASSUMPTIONS
• One dimensional, steady state conduction
• Constant thermal conductivity
SKETCH
PROPERTIES AND CONSTANTS
The thermal conductivity of glass wool at 20°C (k) = 0.036 W/(m K)