Why are Cepheid variables important?
A) Cepheid variables are stars that vary in brightness extremely rapidly as they rotate on their axes.
B) Cepheid variables are stars that brighten and dim with a period that is directly related to the star's luminosity.
C) Cepheids are a type of young galaxy that helps us understand how galaxies form.
D) Cepheids are supermassive stars that we observe because they will soon undergo supernovae.
B) Cepheid variables are stars that brighten and dim with a period that is directly related to the star's luminosity.
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A rescue plane flying horizontally at 72.6 m/s spots a survivor in the ocean 182 m directly below and releases an emergency kit with a parachute. Because of the shape of the parachute, it experiences insignificant horizontal air resistance
If the kit descends with a constant vertical acceleration of 5.82 m/s2, how far away from the survivor will it hit the waves? A) 574 m B) 4.54 km C) 406 m D) 602 m
When water boils, its temperature
a. increases. b. decreases. c. stays constant. d. cannot be determined.
The inductor in a radio receiver carries a current of amplitude 0.200 A when an ac voltage of amplitude 2.40 V is across it at a frequency of 1400 Hz. What is the value of the inductance?
A) 1.43 mH B) 1.36 mH C) 9.20 mH D) 4.42 mH E) 1.97 mH
A truck moving at 36 m/s passes a police car moving at 45 m/s in the opposite direction. If the frequency of the siren is 500 Hz relative to the police car, what is the frequency heard by an observer in the truck after the police car passes the truck? (The speed of sound in air is 343 m/s.)
a. 361 b. 636 c. 393 d. 396 e. 383