The atom 40K decays radioactively to the gas 40Ar. An ancient rock is found to contain enough 40Ar gas to indicate that 77.0% of the 40K in the rock has decayed to 40Ar since the rock solidified
(Any previous argon would have boiled out of liquid rock.) How long ago did the rock solidify? The half-life of 40K is 1.25 billion years.
A) 2.65 billion years
B) 0.471 billion years
C) 1.80 billion years
D) 0.324 billion years
A
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A. 580 N B. 290 N C. 1160 N D. 2320 N E. 1200 N
If we found a solar system where the central star's mass was double that of the Sun, what would be the period a planet orbiting 1 AU from the central star?
A) more than a year B) less than a year C) about a year D) impossible to say, since we need to know the mass of the planet to predict its period
A threaded steel rod (Es 5 210 GPa, dr 5 15 mm, ctes 5 12 3 1026/°C.) is held stress-free between rigid walls by a nut and washer (dw 5 22 mm) assembly at each end. If the allowable bearing stress between the washer and wall is 55 MPa and the allowable normal stress in the rod is 90 MPa, the maximum permissible temperature drop DT is approximately:
(A) 25 8C
(B) 30 8C
(C) 38 8C
(D) 46 8C
Convert 14°C to K
A) 46 K B) 100 K C) 187 K D) 287 K E) 474 K