Rain drops that freeze prior to striking the warm ground is a(n) ______________ storm
a. hail
b. rain
c. ice
d. snow
a
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Hubble's galaxy classification diagram (the "tuning fork")
A) shows how galaxies evolve from one form to another. B) relates galaxies according to their colors and luminosities. C) suggests the existence of black holes. D) relates galaxies according to their shapes.
When charges qa, qb, and qc are placed respectively at the corners a, b, and c of a right triangle, the potential at the midpoint of the hypotenuse is 24 V. When the charge qa is removed, the potential at the midpoint becomes 17 V. When, instead, the charge qb is removed (qa and qc both in place), the potential at the midpoint becomes 13 V. What is the potential at the midpoint if both charges qa
and qc are removed? a. 11 V b. 7.0 V c. 6.0 V d. 18 V e. 17 V
State the general rule for the interaction of magnetic poles
High-strength stainless steel is required for use in building structures and equipment (e.g. , cranes). It is produced by heat treating quench-hardened steel in a process called tempering that reduces brittleness and imparts toughness. In a production facility, alloy steel plates (k=50 W/(m K), c=460 J/(kg K) and ?=7865 kg/m3) of thickness 3 cm have to be tempered in a convective oven by heating them to 5500C. If the plates are initially at 400C and the air inside the heat treating oven is at 7000C with a convective heat transfer coefficient of 45 W/(m2 K), determine how long the plate has to remain in the oven.
GIVEN
• Alloy steel plate of thickness L=3 cm=0.03 m
• Tempering in oven to 5500C
• Initial temperature of the plate (To) = 40°C
• Heat treating oven temperature (T?) = 700°C
• Convective heat transfer coefficient ( ch ) = 45 W/(m2 K)
FIND
• The time required for the plate to reach 5500C.
ASSUMPTIONS
• Constant thermal conductivity
• End effects are negligible
SKETCH
