Rank the following compounds by solubility in water, from most soluble to least
1) CH3CH2OH 2) CH3OCH3 3) CH3CH2NH2
A) 1, 3, 2
B) 1, 2, 3
C) 3, 2, 1
D) 3, 1, 2
E) 2, 1, 3
Answer: A
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Suppose a wheel is initially rotating at 10.0 rad/s while undergoing constant angular acceleration reaching a speed of 30.0 rad/s after 36.0 seconds have elapsed. How long after the initial time has the wheel undergone half of the angular displacement that it will have gone through during the entire 36.0-second interval?
a. 0.556 s b. 22.2 s c. 18.0 s d. 56.5 s
What types of stars end their lives with supernovae?
A) all stars that are red in color B) all stars that are yellow in color C) high-mass stars that can continue to have core fusion until they have iron cores D) stars that are similar in mass to the Sun E) stars that have reached an age of 10 billion years
Surface hardening of metallic machine components, such as ball and roller bearings, is carried out in a heat treatment process where the surface temperature is increased to a desirable level without altering the internal temperature substantially. In one such operation, steel ball (spherical) bearings with a diameter of 25 mm, initially at 25°C, are immersed in a very high temperature (1000°C) molten electrolyte-solution bath and quickly removed when the temperature at a depth of 1 mm from the outer surface of the steel ball attains 725°C. If the convective heat transfer coefficient between the steel ball and the bath liquid is assumed to be 4.95 kW/(m2 K), determine the time required for attaining the surface hardening condition.
GIVEN
Steel ball bearing diameter (d)= 25 mm=0.025 m
Initial temperature (To) = 25°C
Temperature of electrolyte solution (T?) = 1000°C
The heat transfer coefficient (hc) = 4.95 kW/(m2 K) = 4950 W/(m2 K)
Radius of the surface where temperature of 7250C is attained= 11.5 mm
FIND
Time required for attaining temperature of 7250C at depth of 1 mm from outer surface.
ASSUMPTIONS
constant bath temperature, thermal properties and heat transfer coefficient
SKETCH
The most active galactic nuclei are usually found at large distances from us; relatively few nearby galaxies have active galactic nuclei. What does this imply?
A) Supermassive black holes existed only when the universe was young and no longer exist today. B) Active galactic nuclei tend to become less active as they age. C) Active galactic nuclei can form only at large distances from the Milky Way. D) The jets seen in many active galactic nuclei must cause them to move far away from us.