A sphere is constructed of two concentric parts. The inner part is a solid sphere of radius 10.0 cm made of a material with density 4000 kg/m3
The outer part is a spherical shell with inner radius 10.0 cm and outer radius 20.0 cm. The material in the outer shell has a density
9000 kg/m3.
(a) What is the mass of the sphere?
(b) What is the average density of this sphere?
What will be an ideal response?
Answer: (a) 281 kg (b) 8.38 × 103 kg/m3
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What happens when a particle of matter meets its corresponding antiparticle of antimatter?
A) They can form a complete atom. B) The combined mass of the two particles is completely transformed into energy (photons). C) They fuse to make a heavier particle. D) The question makes no sense, since antimatter does not really exist.
An oxygen molecule falls in a vacuum. From what height must it fall so that its kinetic energy at the bottom equals the average energy of an oxygen molecule at 920 K?
A) 36,500 meters B) 12,100 meters C) 24,300 meters D) 48,700 meters
A metal plate is placed in the sunlight. The incident radiant energy G is 780 W/m2. The air and the surroundings are at 10°C. The heat transfer coefficient by natural convection from the upper surface of the plate is 17 W/(m2 K). The plate has an average emissivity of 0.9 at solar wavelengths and 0.1 at long wavelengths. Neglecting conduction losses on the lower surface, determine the equilibrium temperature of the plate.
GIVEN
- A metal plate is sunlight
- Incident radiant energy
- Temperature of air and surroundings
- Natural convection heat transfer coefficient
- Plate emissivity (?) = 0.9 at solar wavelengths, 0.1 at long wavelengths
FIND
-The equilibrium temperature of the plate (Tp)
ASSUMPTIONS
- Steady state
- Conduction losses on the lower surface of the plate are negligible
- The surroundings behave as a blackbody enclosure
SKETCH
PROPERTIES AND CONSTANTS
the Stephan-Boltzmann constant
If a bar magnet is falling through a loop of wire, the induced current in the loop of wire sets up a field which exerts a force on the magnet. This force between the magnet and the loop will be attractive when
a. the magnet enters the loop. b. the magnet is halfway through. c. the magnet is leaving the loop. d. never.