The primary source of the Sun's energy is
A) oxidation of carbon in the core.
B) dark energy.
C) gravitational collapse of the helium towards the core.
D) the weak force creating energy from uranium decay.
E) the strong force fusing hydrogen into helium.
E
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The speed of light is about 300,000 km/s (3 × 105 km/s). How far does light travel in 30 seconds?
A) 300 thousand km (300,000, or 3 × 105 km) B) 9 million km (9,000,000, or 9 × 106 km) C) 10 thousand km (10,000, or 106 km) D) 900 thousand km (900,000, or 9 × 105 km)
Where are neutrons found in the hydrogen atom?
a. nucleus b. cloud surrounding the nucleus c. outside the atom d. None of the other choices are correct.
The percentage of 235U, as a fraction of the total uranium content, in a uranium fission bomb is closest to
A) 50 percent. B) 20 percent. C) 1 percent. D) 90 percent. E) 5 percent.
Radiation: A blacksmith is flattening a steel plate having dimensions 10 cm × 15 cm × 1 mm. He has heated the plate to 900 K. If the emissivity of the plate is 0.75, at what rate does it lose energy by radiation? Ignore any heat exchange with the surroundings. (? = 5.67 × 10-8 W/m2 ? K4)
A. 360 W B. 760 W C. 790 W D. 850 W E. 880 W