Mike Huskey wrote:

> What kind of energy would it take to make a planet explode in a matter
> of seconds, if it is even possible? Assume that the planet is like
> Earth if it will make your calculations easier.

The amount of energy required to completely gravitationally disrupt a body
-- that is, give each little bit of mass escape velocity from every other
little bit of mass -- is called the gravitational binding energy, and for a
uniform, spherical mass, is 

    U = (3/5) G M^2/R.

With the assumption that the Earth is uniform (incorrect, but sufficient to
get an order-of-magnitude estimate), with M = 5.97 x 10^24 kg and R = 6.37
x 10^6 m, U is 2.24 x 10^32 J.  By comparison, the Sun's luminosity is
about 4 x 10^26 W; the gravitational binding energy of the Earth is equal
to about a week of the Sun's total energy output.

[ed. note: the proportion of the Sun's output that falls on the Earth is
 roughly 2 x 10^-9, giving 2 x 10^17 W, so 2.24 x 10^32 J is equal to all
 the solar energy that the Earth receives in 35 million years or so]

Now to make it happen in "a matter of seconds" you need to apply even more
energy.  The only real limitation there is the speed of light.  (Any waves
travelling through the body itself are going to be shockwaves, not sound
waves.)

-- 
        Erik Max Francis, &tSftDotIotE / email:  max@alcyone.com
                      Alcyone Systems /   web:  http://www.alcyone.com/max/
 San Jose, California, United States /  icbm:  37 20 07 N  121 53 38 W
                                    \
               "I am become death, / destroyer of worlds."
                                  / J. Robert Oppenheimer (quoting legend)