The main source of energy for a star as it grows in size to become a red giant is ________
A) hydrogen fusion in a shell surrounding the central core
B) gravitational contraction
C) helium fusion in the central core
D) hydrogen fusion in the central core
A
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A steel bar of rectangular cross section (a 5 38 mm, b 5 50 mm) carries a tensile load P. The allowable stresses in tension and shear are 100 MPa and 48 MPa, respectively. The maximum permissible load Pmax is approximately:
(A) 56 kN
(B) 62 kN
(C) 74 kN
(D) 91 kN
In a physical fitness program, a woman who weighs 510 N runs up four flights of stairs in 22 s. Each flight rises 3.1 m
(1 hp = 746 W) (a) What is her total change in potential energy? (b) What was the minimum average power (in watts) that she expended during the 22 s? (c) What horsepower motor would be required to generate the same power?
Radio astronomers often study the radiation emitted by a hydrogen atom from a transition between the two hyperfine levels associated with the ground state. This radiation has a wavelength of 21 cm
What is the energy difference between the hyperfine levels? (1 eV = 1.60 × 10-19 J) A) 5.9 × 10-6 eV B) 5.9 × 10-25 J C) 1.7 × 10-24 J D) 4.7 × 10-25 J
A 0.30-?F capacitor is connected to a 400-V battery. What potential energy is stored in the capacitor?
a. 1.3 × 10^?3 J b. 6.0 × 10^?4 J c. 4.8 J d. 0.024 J e. 0.048 J