A force is a vector quantity because it has both
A) magnitude and direction.
B) mass and velocity.
C) action and reaction counterparts.
D) speed and direction.
Answer: A
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A wire of perimeter P and cross-sectional area A emerges from a die at a temperature T (above ambient temperature) and with a velocity U. Determine the temperature distribution along the wire in the steady state if the exposed length downstream from the die is quite long. State clearly and try to justify all assumptions.
GIVEN
• A wire emerging from a die at a temperature (T) above ambient
• Wire perimeter = P
• Cross-sectional area = A
• Wire emerges at a temperature T above ambient
• Wire velocity = U
FIND
• The temperature distribution along the wire in the steady state if the exposed length downstream from the die is quite long. State clearly and try to justify all assumptions
ASSUMPTIONS
• Ambient temperature is constant at T?
• Heat transfer coefficient between the wire and the air is uniform and constant at hc
• The material properties of the wire are constant
? Thermal conductivity = k
? Thermal diffusivity = ?
• Axial conduction only
• Wire temperature is uniform at a cross section (negligible internal thermal resistance)
SKETCH
Suppose that an ancient civilization had built a stone structure 6000 years ago to point towards a bright star as it rose
Would that structure still point at that star today? If not, why not, and what information would archaeoastronomers need to figure out which star the structure pointed at?
How necessary is soap for removing salt from your hands?
A) Soap is necessary because it has both a polar and nonpolar end to interact with the positive and negative ions in the salt. B) Soap is necessary because it creates a film on the surface of your skin, shielding it from interacting with the ionic charges of the salt. C) Soap is not at all necessary for removing salt from your hands. The strong ion-dipole interactions between fresh water and the salt are most sufficient to lift the salt away from your hands. D) Soap is not necessary because there are no electrical charges on the skin of your hands for the salt to interact with.