Dark energy accounts for about 70% of the critical density of the Universe
a. True
b. False
Indicate whether the statement is true or false
True
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What primary wavelength and corresponding photon energy is emitted by a body at:
(a) 400.°C? (b) 800.°C? (c) 1200.°C?
A satellite is placed in a geosynchronous orbit. In this equatorial orbit with a period of 24 hours, the satellite hovers over one point on the equator. Which statement is true for a satellite in such an orbit?
a. There is no gravitational force on the satellite. b. There is no acceleration toward the center of the Earth. c. The satellite is in a state of free fall toward the Earth. d. There is a tangential force that helps the satellite keep up with the rotation of the Earth. e. The force toward the center of the Earth is balanced by a force away from the center of the Earth.
Of the thousands of different isotopes known to exist,
a. most of them are radioactive. b. only a couple can be used to build an atom bomb. c. some are used in medical diagnosis and treatment. d. most occur naturally. e. all of the above
An object of mass m is hung from a string and set swinging. The period of the oscillation is recorded as T. The object of mass m is removed and is replaced by an object of mass 2m. When this object is set swinging, the period of its motion is
1. 2T 2. T/2 3. ?2T 4. T