Jill is farsighted and cannot see objects clearly that are closer to the eye than 80.0 cm. What is the focal length of the contact lenses that will enable her to see objects at a distance of 25.0 cm from her eyes?
A)
+36.4 cm
B)
-36.4 cm
C)
-21.2 cm
D)
+21.2 cm
E)
+32.5 cm
A
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A group of 10 to 100 stars that formed at the same time but are so widely scattered in space their mutual gravity cannot hold them together is called
a. a globular cluster. b. an open cluster. c. an association. d. a spherical component e. an accretion disk.
The great contribution of Tycho Brahe was to
A) observe planetary positions with sufficient accuracy that later enabled Kepler to discover the laws of planetary motion. B) discover four moons orbiting Jupiter, thereby lending strong support to the idea that the Earth is not the center of the universe. C) offer the first detailed model of a Sun-centered solar system, thereby beginning the process of overturning the Earth-centered model of the Greeks. D) discover that planets orbit the Sun in elliptical orbits with varying speed.
The Doppler technique can be used to estimate the semimajor axis of a planet's orbit by
A) measuring the time it takes for the star's line-of-sight velocity to cycle from peak to peak, and using Newton's version of Kepler's Third law. B) measuring the speed at which the star orbits the mutual center-of-mass of the star and planet, and using Newton's theory of gravity. C) measuring the asymmetries in the velocity curve. D) measuring the amount by which the starlight is reduced when the planet transits.
The color force between quarks is carried by
a. mesons b. the strong force c. leptons d. gluons e. none of the above