After one half-life, a sample of a particular
radioactive material
a) is twice as massive as the original sample of material.
b) has its half-life reduced by one half.
c) has only half the original activity.
d) is no longer radioactive at all.
c
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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
What evidence from the careful examination of impact craters provides evidence that Mars had surface water long ago?
A) indistinct rims of many large craters due to water erosion B) lack of small craters which would have been erased by ancient rainfall C) channels where water once flowed between crater lakes D) all of these
A boat floating in a large pool is loaded with solid iron bars. The water level at the pool's edge is marked with a red line. The iron is now thrown overboard. When the water becomes calm again,
A. the red line is slightly lower than the water level. B. the red line is still at the water level. C. the red line is slightly higher than the water level.
A light emitting diode emits light of approximate wavelength 670 nm. What is the band gap?
A) 1.86 eV B) 4.14 eV C) 1.80 eV D) 3.72 eV E) 2.70 eV