A child is standing at the rim of a disk holding a rock. The disk rotates freely without friction. At the instant shown, the child throws the rock radially outward. Which of the indicated paths most nearly represents the trajectory of the rock as seen from above?
4
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When an object floats in a liquid, the buoyant force is __________ the weight of the object
Fill in the blank(s) with correct word
There is almost no hydrogen gas in the atmosphere because
A. it escapes the Earth's gravity B. there is very little hydrogen in the oceans or land C. hydrogen molecules move slower than oxygen and nitrogen D. hydrogen has all sunk to the Earth's core
Two coaxial parallel plate discs are situated relative to each other as shown in the sketch. The diameter of the upper plate is 20 cm, and that of the lower plate is 40 cm. The lower plate is maintained at a uniform temperature of 500 K and the upper temperature is maintained at 456 K. To maintain these relative temperatures, a heater has to be installed in the upper plate. Assuming an environmental temperature of the surroundings at 300 K, determine the power necessary of the heater in the upper plate to maintain the two constant plate temperatures under steady state conditions.
GIVEN
• Two coaxial parallel plate discs at distance of L = 20 cm=0.2 m
• Upper plate diameter (D1) = 20 cm = 0.2 m
• Lower plate diameter (D2) = 40 cm = 0.4 m
• Upper plate temperature (T1) = 456 K
• Lower plate temperature (T2) = 500 K
• Surrounding temperature (Tsurr) = 300 K
FIND
(a) Power necessary of the heater in upper plate to maintain the constant plate temperatures under steady state conditions.
SKETCH
PROPERTIES AND CONSTANTS
The Stephan-Boltzmann constant (?) = 5.67 × 10–8 W/(m2 K4)
The lunar highlands have more craters than the maria because ________.
A. the surface of the maria is liquid and craters quickly disappear there B. the maria are much older than the highlands C. the material composing the highlands is very soft and easily cratered D. the maria are much younger than the highlands