A fast-moving body must have a larger acceleration than a slow-moving body
a. True
b. False
Indicate whether the statement is true or false
False
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In cryogenic surgery, a small spherical probe is brought into contact with the diseased tissue which is frozen and thereby destroyed. One such probe can be modeled as a 3-mm diameter sphere whose surface is maintained at 240 K when the surrounding tissue is at 314 K. During the surgical procedure, a thin layer of tissue freezes around the probe at a temperature of 273 K. Assuming that the thermal conductivity of a frozen tissue is 1.5 W/(m K) and the heat transfer mechanism at the surface is described by the effective convective coefficient of 50 W/(m2 K), estimate the thickness of frozen tissue formed during a 30 min long operation.
GIVEN
Diameter of sphere(D1)= 3 mm, r1=0.0015 m
Probe surface temperature(Tp)= 240 K
Surrounding tissue temperature(Tt)= 314 K
Tissue freezing temperature(Tf)= 273 K
Thermal conductivity of frozen tissue(kt)= 1.5 W/(m K)
Effective convective coefficient (h?)=50 W/(m2 K)
Operation time (t)= 30 min
FIND
Thickness of a frozen tissue formed
ASSUMPTIONS
1 dimensional Steady state conditions persist
Negligible contact resistance between probe and frozen tissue.
Constant properties.
SKETCH
The planet that is normally farthest from the Sun, but sometimes is not, is ______________
Fill in the blank(s) with correct word
Far-infrared astronomy must be done from high-flying aircraft because:
A) far-infrared radiation never reaches Earth's surface. B) far-infrared photons are highly energetic. C) far-infrared telescopes have zero diffraction fringe. D) far-infrared sources are very bright.
Why is Saturn almost as large in radius as Jupiter despite its smaller mass?
A) Jupiter's greater mass compresses it more, thus increasing its density. B) Saturn's rings make the planet look bigger. C) Saturn is farther from the Sun, thus cooler, and therefore less compact. D) Saturn has a larger proportion of hydrogen and helium than Jupiter, and is therefore less dense. E) Jupiter's strong magnetic field constrains its size.