An object is thrown vertically and accelerates downward at +9.80 m/s2 (downward is positive and upward is negative)
(a) What is its displacement after 5.00 s if it starts at 2.50 m/s?
(b) How fast is it moving after that 5.00 s?
(a) 135. meters
(b) 46.5 m/s
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A star with the mass of our Sun will go through several stages of energy generation through fusion. Which sequence accurately describes these stages in the correct order?
a. hydrogen core ? hydrogen shell ? helium shell ? helium core b. hydrogen core ? helium core ? hydrogen shell ? helium shell c. hydrogen core ? hydrogen shell ? helium core ? helium shell ? carbon core d. hydrogen core ? hydrogen shell ? helium core ? helium shell e. hydrogen shell ? hydrogen core ? helium shell ? helium core
If no force is applied to a moving object, it will continue to move with constant speed in a straight line
Indicate whether the statement is true or false
A light oil flows through a copper tube of 2.6-cm-ID and 3.2-cm-OD. Air flows perpendicular over the exterior of the tube as shown in the following sketch. The convection heat transfer coefficient for the oil is 120 W/(m2 K) and for the air is 35 W/(m2 K). Calculate the overall heat transfer coefficient based on the outside area of the tube (a) considering the thermal resistance of the tube, (b) neglecting the resistance of the tube but assume that fouling factors of 0.0009 (m2 K)/W and 0.0004 (m2K)/W have developed on the inside and on the outside, respectively.
GIVEN
• Air flow over a copper tube with oil flow within the tube
• Tube diameters: Inside (Di) = 2.6 cm = 0.026 m
Outside (Do) = 3.2 cm = 0.032 m
• Convective heat transfer coefficients: Oil h i= 120 W/(m2 K) Air h o= 35 W/(m2 K)
• Fouling factors: Inside (Rdi) = 0.0009 (m2 K)/W
Outside (Rdo) = 0.0004 (m2 K)/W
FIND
• The overall heat transfer coefficient based on the outside tube area (Uo),
(a) considering the thermal resistance of the tube, and
(b) neglecting the tube resistance
ASSUMPTIONS
• Uniform heat transfer coefficients
• Variation of thermal properties is negligible
SKETCH
PROPERTIES AND CONSTANTS
the thermal conductivity of copper (k) = 392 W/(m K) (at 127°C)
A partial solar eclipse occurs for people in the Sun's
A) umbra. B) penumbra. C) none of these