Why must both parallax and proper motion be known to give transverse velocity?
What will be an ideal response?
To turn the star's apparent motion across our line of sight into its real velocity in that direction, we also need to know the actual distance from parallax data.
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A microphone records sound produced from two speakers in a room with no other sound sources. If the intensity of one of the sound waves at a given location is 0.055 W/m2 and if the microphone receives a minimum intensity of 0.004 
when both speakers are active what is a possible value for the intensity of the other source at the microphone’s location?
A. Need more info to solve.
B. 0.088 
C. 0.051
D. 0.048
Open spaces in ice crystals contribute to
A) decreased density. B) increased density. C) neither of these
Three essential components of a nuclear reactor are: a fissionable fuel ,a coolant to transfer the heat, and
A) a "scrubber" to prevent radioactive isotopes from getting into the environment. B) a radioactive substance to keep the reaction going. C) tritium to speed up the neutrons. D) control rods. E) lead to stop the neutrons.
The period of a pendulum is 2.0 s in a stationary inertial frame of reference. What is its period when measured by an observer moving at a speed of 0.80c with respect to the inertial frame of reference?
a. 1.6 s c. 2.5 s b. 1.2 s d. 3.3 s