All real images
a. cannot be focused on a screen.
b. are erect.
c. can be focused on a screen.
d. are inverted.
c
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The adoption of very similar streamlined body shapes by both sharks and dolphins provides evidence for
A) cross-breeding B) convergent evolution C) genetic mutations D) life originating in the oceans
The most accurate measurements known are
A) mass measurements. B) measurements of electric charge. C) spectroscopic measurements. D) made with thermometers.
A thermocouple (0.8-mm-OD) is located horizontally in a large enclosure whose walls are at 37°C. The enclosure is filled with a transparent quiescent gas that has the same properties as air. The electromotive force (emf) of the thermocouple indicates a temperature of 230°C. Estimate the true gas temperature if the emissivity of the thermocouple is 0.8.
GIVEN
• Horizontal thermocouple in a large enclosure
• Thermocouple outside diameter (D) = 0.8 mm = 0.0008 m
• Enclosure wall temperature (Te) = 37°C = 310 K
• Gas is enclosure is quiescent and has the same properties as air
• Thermocouple reading (Ttc) = 230°C = 503 K
• Thermocouple emissivity (?) = 0.8
FIND
• True gas temperature (T?)
ASSUMPTIONS
• Enclosure behaves as a black body
• Conduction along the thermocouple out of the enclosure is negligible
SKETCH
PROPERTIES AND CONSTANTS
The Stephan-Boltzmann Constant (?) = 5.67 ?10–8 W/(m2 K4).
The kinetic friction force that a horizontal surface exerts on a 60.0-kg object is 50.0 N. If the initial speed of the object is 25.0 m/s, what distance will it slide before coming to a stop?
A) 15.0 m B) 30.0 m C) 375 m D) 750 m