How many radioactive atoms are present in a sample that has an activity of 0.5 ?Ci and a half-life of 10 years? (1 curie = 3.7 × 10^10 decays/s)
a. 9.5 × 10^12 atoms
b. 8.4 × 10^12 atoms
c. 7.3 × 10^12 atoms
d. 6.5 × 10^12 atoms
e. 2.7 × 10^5 atoms
b
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A magnifying lens has a focal length of 10 cm. A person has a near point of 25 cm
(a) What is the magnification of the lens for that person when their eyes are focused at infinity? (b) What is the magnification of the lens for that person when their eyes are focused at their near point?
Rays from a distant object do not diverge enough for a nearsighted person to focus; this can be corrected with a
A. converging or positive lens. B. diverging or positive lens. C. converging or negative lens. D. diverging or negative lens.
Which of the following is not one of the three major strategies used to measure the mass of a galaxy cluster?
A) measuring the speeds of galaxies orbiting the cluster's center B) studying x-ray emission from hot gas inside the cluster C) observing how the cluster bends light from galaxies located behind it D) measuring the temperatures of stars in the halos of the galaxies
A 4.0-kg block is lowered down a 37° incline a distance of 5.0 m from point A to point B. A horizontal force (F = 10 N) is applied to the block between A and B as shown in the figure. The kinetic energy of the block at A is 10 J and at B it is 20 J. How much work is done on the block by the force of friction between A and B?
a.
?58 J
b.
?53 J
c.
?68 J
d.
?63 J
e.
?47 J