Astronomers can measure a star's mass in only certain cases. Which one of the following cases might allow astronomers to measure a star's mass?
A) We know the star's luminosity and distance. B) The star is of spectral type G.
C) The star is a member of a binary star system. D) The star is of spectral type A.
C
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A force of 15.2 N directed along the positive x-axis combines with a second force to produce a total force vector of magnitude 17.9 N. What is the magnitude of the second vector?
A. Not enough information is given. B. 9.5 N C. 23.5 N D. 2.7 N
If bits of the coals do not stick to your feet while walking barefoot on red-hot coals, it would be best if your feet are
A) wet. B) dry. C) warm. D) cold. E) very hot.
A gasoline engine absorbs 2500 J of heat at 250°C and expels 2000 J at a temperature of 50°C. What is the magnitude of the change in entropy (in J/K) for the system?
a. 6.2 b. 4.7 c. 1.4 d. 10.9 e. 3.2
An unusual lightning strike has a vertical portion with a positive current of +400 A upwards. The Earth's magnetic field at that location is parallel to the ground and has a magnitude of 30 ?T. In N, the force exerted by the Earth's magnetic field on the 25-m-long current is
a. 0. b. 0.012 N, East. c. 0.012 N, West. d. 0.30 N, West. e. 300 N, East.