Two nuclei may have equal Z, but different A, because they contain
a. equal numbers of protons and neutrons.
b. equal numbers of protons but different numbers of neutrons.
c. different numbers of protons but equal numbers of neutrons.
d. different numbers of protons and neutrons.
e. electrons as well as neutrons.
b
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Gravitational Potential Energy: How high a hill would a 75-kg hiker have to climb to increase her gravitational potential energy by 10,000 J?
Fill in the blank(s) with the appropriate word(s).
Vision Problems: A little known fact is that both Robinson Crusoe and Friday wore eyeglasses. As it so happens, Robinson Crusoe was farsighted while Friday was nearsighted. Whose eyeglasses did they use whenever they wanted to start a fire by focusing the sun's rays?
A. Robinson Crusoe's B. Friday's C. Both would work equally well. D. Both actually worked, but Friday's was a little bit better. E. Neither's worked, but fortunately they were in possession of matches.
Evidence that the universe is expanding is provided by Hubble's Law which states that
A. the farther away a star is from us, the less its luminosity. B. the farther away a star is from us, the less its velocity of recession. C. the farther away a star is from us, the greater its velocity of recession. D. the nearer to us a star is, the greater its velocity of recession.
A flat plate solar collector of 3 m ? 5 m area has an absorber plate that is to operate at a temperature of 70°C. To reduce heat losses, a glass cover is placed 0.05 m from the absorber. Its operating temperature is estimated to be 35°C. Determine the rate of heat loss from the absorber if the 3 m edge is tilted at angles of inclination from the horizontal of 0°, 30°, and 60°.
GIVEN
• A flat plate solar collector
• Area = 3 m × 5 m
• Absorber temperature (Ta) = 70°C
• Glass cover temperature (Tc) = 30°C
• Distance between absorber and cover (?) = 0.05 m
FIND
Heat loss by natural convection from the absorber of angles (?) of (a) 0°, (b) 30°, and (c) 60° from the horizontal
ASSUMPTIONS
• The space is air filled
SKETCH
PROPERTIES AND CONSTANTS
for dry air at the mean temperature of 52.5°C
Thermal expansion coefficient (?) = 0.00307 1/K
Thermal conductivity (k) = 0.0274 W/(m K)
Kinematic viscosity (?) = 18.7 × 10–6 m2/s
Prandtl number (Pr) = 0.71