Briefly summarize current knowledge about the term flife in the equation Number of Civilizations = Np × flife × fcivilization × fnow
What will be an ideal response?
We know that at least one planet within its star's habitability zone has developed life—Earth. Beyond that, we have no real evidence on which to base an estimate of the value of flife.
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Waves on a String: The speed of sound in steel is 5000 m/s. What is the wavelength of a sound wave of frequency 660 Hz in steel?
A. 7.58 m B. 2.41 m C. 1.21 m D. 0.829 m E. 0.132 m
Motional Emf: A conducting rod whose length is ? = 27.0 cm is placed on frictionless U-shaped metal rails that is connected to a lightbulb having a resistance of 5.00 ? as shown in the figure. The rails and the rod are in the plane of the page. A constant uniform magnetic field of strength 1.20 T is applied perpendicular to and out of the paper. An external applied force moves the rod to the right with a constant speed. At what speed should the rod be pulled so that the lightbulb will consume energy at a rate of 1.10 W?
A. 2.00 m/s B. 3.50 m/s C. 4.26 m/s D. 6.00 m/s E. 7.24 m/s
Which of the following is smallest?
A) size of a typical planet B) 1 light-second C) 1 AU D) size of a typical star
A concave mirror has a focal length of 20 cm. What is the position (in cm) of the resulting image if the image is inverted and four times smaller than the object?
a. 15 b. 25 c. 50 d. 100 e. ?15