The kinetic energy of an object is given by:
[tex]K= \frac{1}{2}mv^2 [/tex]
where
K is the kinetic energy
m is the mass of the object
v is its velocity.
The comet in our problem has a mass of [tex]m=7.85 \cdot 10^{11} kg[/tex] and a velocity of [tex]v=25000 m/s[/tex], so its kinetic energy is:
[tex]K= \frac{1}{2}(7.85 \cdot 10^{11} kg)(25000 m/s)^2=2.45 \cdot 10^{20}J [/tex]
