If the Moon crosses Earth's shadow at the center of the umbra, how long will the entire eclipse last from start to finish?
a. 2 to 3 minutes
b. 7 minutes
c. 1 hour 45 minutes
d. 2 hours
e. 6 hours
e
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A spherical mirror
A. is shaped like a complete sphere. B. is a section of a sphere. C. creates only spherical images. D. only reflects spherical rays.
Which of the following is the origin of most of the large moons around the jovian planets?
A) They are captured asteroids. B) They are captured comets. C) They are captured planets. D) They were formed by condensation and accretion in a disk of gas around the planet. E) They were formed by giant impacts.
Calculate the rate of heat transfer through the composite wall in the temperature difference is 25°C and the contact resistance between the sheets of wood is 0.005 m2 K/W
GIVEN
• Wood wall
? Two layers 0.025-m-thick each, nailed together
• Nail cross sectional area of nails = 0.5% of wall area
• Temperature difference (?T) = 20°C
• Contact resistance (A Ri) = 0.005 (m2 K)/W FIND
• The rate of heat transfer through the wall
ASSUMPTIONS
• One dimensional heat transfer through the wall
• Steady state prevails
SKETCH
PROPERTIES AND CONSTANTS
? Wood (Pine) (kw) = 0.15 W/(m K)
? Mild steel (1% C) (ks) = 43 W/(m K)
Atomic Nucleus: In the first nuclear reaction observed, physicists saw an alpha particle (Z = 2) interact with a nitrogen nucleus in air (Z = 7) to produce a proton. The energy of the alpha particle was 55 MeV, enough to enable the nuclei to touch in spite of the Coulomb repulsion. What distance (in fm) between the centers of the alpha particle and the nitrogen was reached? This determines a limit on the radius of the nitrogen nucleus. (1 eV = 1.60 × 10-19 J, e = 1.60 × 10-19 C, 1/4??0 = 8.99 × 109 N ? m2/C2)
A. 0.37 fm B. 0.18 fm C. 0.05 fm D. 158.40 fm