The average mass of each neutron in the nucleus of an iron atom is not the same as the average mass of each neutron in the nucleus of a gold atom
Indicate whether the statement is true or false
T
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A large billet of steel initially at 260°C is placed in a radiant furnace where the surface temperature is held at 1200°C. Assuming the billet to be infinite in extent, compute the temperature at point P shown in the accompanying sketch after 25 min have elapsed. The average properties of steel are: k = 28 W/(m K), p = 7360 kg/m3, and c = 500 J/(kg K).
GIVEN
A large billet of steel is placed in a radiant furnace
Initial temperature (To) = 260°C
Surface temperature of billet in the oven (Ts) = 1200°C
Lapse time (t) = 25 min = 1500 s
Thermal conductivity (k) = 28 W/(m K)
Density (p) = 7360 kg/m3
Specific heat (c) = 500 J/(kg K)
FIND
The temperature at point P shown in the accompanying sketch
ASSUMPTIONS
The billet infinite in extent
SKETCH
In each of the processes described below, energy flows across the boundary of the object that serves as the subject of each sentence. Is this energy flow heat (A), work (B), or some other kind of energy transfer (E)?
(a) The sun emits light into space. (b) You get cooler when standing in the breeze from a fan. (c) Your car’s brakes get hot when used repeatedly. (d) Your hands get warm when you rub them together. (e) Your pizza gets warm in the microwave.
At the upper right of the Hertzprung—Russell diagram we find
A) red giant stars B) supergiant stars C) white dwarfs D) main sequence stars
Given a concave mirror, rays of light originating from the center of curvature reflect off the mirror and focus at
A) 2 R from the mirror. B) the focal point. C) the center of curvature. D) infinity.