A bar magnet is attached solidly to a frictionless surface and its length is aligned with the x axis. To the right of the first magnet a short distance away is a second bar magnet with its center placed on the x axis and its length perpendicular to the x axis. The second magnet is free to move. Once placed in position at rest, which best describes the initial motion of the second magnet?
a. The magnet will move away from the fixed magnet.
b. The magnet will not move.
c. The magnet will move toward the fixed magnet.
d. The magnet will start to rotate.
d
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The moon has an angular diameter of 0.5°. What is the moon's angular diameter in minutes of arc?
a. 0.5 b. 30 c. 50 d. 1800 e. 60.5
A person having a near point of 25 cm and a far point at infinity uses a converging lens of focal length 5.0 cm as a magnifying glass. What is the magnification if the person's eye is relaxed (with the image at his far point)?
What will be an ideal response?
Satellite Motion: A satellite of mass M takes time T to orbit a planet. If the satellite had twice as much mass, the time for it to orbit the planet at the same altitude would be
A. 4T. B. 2T. C. T. D. T/2. E. T/4.
A circular ice skating rink, 20 m in diameter, is enclosed by a large hemispherical dome of diameter 30 m. Assuming that the ice is 2 cm thick, estimate the time it takes for the ice to melt if the refrigeration system of the rink fails. Make this calculation first with both the dome and the ice behaving as black bodies at respective temperatures of 20°C and 0°C. Then repeat with the water-ice having an emissivity of 0.3 and losing heat by natural convection to the air in the dome with a convection heat transfer coefficient of 15 W/(m2 K).
GIVEN
• Circular skating rink enclosed by hemispherical dome
• Diameter of the rink (D1) = 20 m
• Diameter of hemispherical dome (D2)= 30 m
• Temperature of dome and surrounding air (T2)= 200C
• Temperature of ice (T1) = 00C
FIND
Time it takes for ice to melt if the refrigeration system of rink fails considering (a) both dome and ice behaving as black bodies. (b) ice having emissivity of 0.3 and loosing heat by natural convection to air in dome with 2 15 W/(m K)
SKETCH
PROPERTIES AND CONSTANTS
Latent Stefan-Boltzman’s heat of fusion constant for ice (Lf)= (? 334 KJ/kg )=5.67*10-8 W/(m2 K4)