The theory of nuclear astrophysics is that all the heavy elements like uranium are formed in the interior of massive stars. These stars eventually explode, releasing these elements into space. If we assume that at the time of the explosion there were
equal amount of U-235 and U-238, how long ago did the star(s) explode that released the elements that formed our Earth? The present U-235/U-238 ratio is 0.0070 . [The half-lives of U-235 and U-238 are 0.7 × 10^9 yr and 4.47 × 10^9 yr.]
5.9 billion years
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Which of the following types of electromagnetic radiation has the lowest energy?
a. x-rays b. visible light c. ultraviolet d. gamma-rays e. infrared radiation
Mike applied 10 N of force over 3 m in 10 seconds. Joe applied the same force over the same distance in 1 minute. Who did more work?
a) Mike b) Joe c) both did the same work
A block slides on a rough horizontal surface from point A to point B. A force (magnitude P = 2.0 N) acts on the block between A and B, as shown. Points A and B are 1.5 m apart. If the kinetic energies of the block at A and B are 5.0 J and 4.0 J, respectively, how much work is done on the block by the force of friction as the block moves from A to B?
A. ?3.3 J B. +1.3 J C. +3.3 J D. ?1.3 J E. +4.6 J
The horizontal speed of a projectile
a. is zero b. stays constant c. continuously increases d. continuously decreases e. sometimes decreases and sometimes increases