Intensity: Light from a laser forms a 1.31-mm diameter spot on a wall. If the light intensity in the spot is 1.58 × 104 W/m2, what is the power output of the laser? Assume that all the light emitted by the laser hits the spot.
A. 21.3 mW
B. 13.2 mW
C. 17.9 mW
D. 24.7 mW
Answer: A
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Two marbles are rolling along parallel tracks (which may or may not be inclined). A stroboscopic photograph showing a top view of the positions of the marbles at equally spaced instants of time looks like this: At what instant(s) of time do the marbles have the same instantaneous velocity?
A. At time tB
B. At time tG
C. At both tB and tG
D. Some instant between tC and tD
E. Some instant between tD and tE
F. Roughly time tD
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(b) How much work is done by the gravitational force on the block during this displacement? (c) How much work is done by the normal force? (d) What is the speed of the block (assume that it is zero initially) after this displacement?
Which of the following forces are exerted on a satellite that is in orbit around Earth?
A. an attractive gravitational force directed toward the center of Earth B. a force in the direction of the satellite's motion C. an outward force directed away from the center of Earth D. a and b
What characteristic of a star cluster is used to determine its age?
A) the ratio of main sequence to white dwarfs stars B) the number of red giants C) the faintest stars seen in the cluster D) the main sequence turnoff E) the total number of stars in the cluster