A high fountain of water is in the center of a circular pool of water. You walk the circumference of the pool and measure it to be 170 meters. You then stand at the edge of the pool and use a protractor to gauge the angle of elevation of the top of the fountain. It is 51°. How high is the fountain?
a. 17 m
c. 30 m
b. 23 m
d. 33 m
D
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The Sun's elliptical shape at sunset can be adequately explained by
A) Fermat's principle. B) the law of refraction. C) both of these D) neither of these
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
Which of the following statements about the sunspot cycle is not true?
A) The number of sunspots peaks approximately every 11 years. B) With each subsequent peak in the number of sunspots, the magnetic polarity of the Sun is the reverse of the previous peak. C) The rate of nuclear fusion in the Sun peaks about every 11 years. D) The cycle is truly a cycle of magnetic activity, and variations in the number of sunspots are only one manifestation of the cycle. E) The number of solar flares peaks about every 11 years.
A bicycle has wheels that are 60 cm in diameter. What is the angular speed of these wheels when it is moving at 4.0 m/s?
A) 1.2 rad/s B) 4.8 rad/s C) 0.36 rad/s D) 13 rad/s E) 7.6 rad/s