To make Helium-4 you need what?
A.) 4 protons.
B.) 2 protons and 2 neutrons.
C.) 2 protons and 4 neutrons.
D.) 4 neutrons.
E.) 1 proton and 3 neutrons.
Answer: B.) 2 protons and 2 neutrons.
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Which of the following can't be associated with the spiral arms of a galaxy?
a. Dust and gas b. Metal poor stars c. Young, massive stars d. Star formation
Photoelectric Effect: A photocathode having a work function of 2.8 eV is illuminated with monochromatic electromagnetic radiation whose photon energy is 4.0 eV. What is the threshold (cutoff) frequency for photoelectron production? (1 eV = 1.60 × 10-19 J, h = 6.626 × 10-34 J ? s)
A. 6.8 × 1014 Hz B. 2.9 × 1014 Hz C. 7.7 × 1014 Hz D. 8.6 × 1014 Hz E. 9.7 × 1014 Hz
Why are there two tails to some comets?
A. The "dust tail" is formed by solar radiation pressure. The "gas tail," is pushed out by the solar wind. B. The "gas tail" is formed by solar radiation pressure. The "dust tail," is pushed out by the solar wind. C. Comets contain dense material which is attracted by the Sun's gravity, forming a tail which points toward the Sun. D. The statement is false: comets have only one tail.
A truck moves 70 m west, then moves 120 m east, and finally moves west again a distance of 90 m. If east is chosen as the positive direction, what is the truck's resultant displacement?
a. 40 m c. 280 m b. - 40 m d. -280 m