Final answer:
The kinetic energy of a 9 kg rock would be greater than that of a 3 kg rock if they have the same velocity.
Step-by-step explanation:
In physics, the kinetic energy of an object is given by the equation KE = 1/2mv^2, where KE is the kinetic energy, m is the mass of the object, and v is the velocity of the object.
In the given question, if we compare a 3 kg rock and a 9 kg rock, assuming they have the same velocity, we can see that the kinetic energy of the 9 kg rock will be greater than that of the 3 kg rock. This is because the mass is directly proportional to the kinetic energy.