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 × 109 yr and 4.47 × 109 yr.]

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The dipole moment of the water molecule (h2o) is 6.17x10^-30 c.m. consider a water molecule located at the origin whose dipole moment p points in the +x-direction. a chlorine ion ( of charge-1.60x10^-19c , is located at x=3.00x10^-9m . assume that is much larger than the separation d between the charges in the dipole, so that the approximate expression for the electric field along the dipole axis can be used. a) find the magnitude of the electric force that the water molecule exerts on the chlorine ion. b) what is the direction of the electric force. -x-direction or +x-direction c) is this force attractive or repulsive?

What is the relationship between wavelength of light and the quantity of energy per photon?