Answer: 5.42 kg
Step-by-step explanation:
The formula for kinetic energy is:
KE = 1/2 * m * v^2
where KE is the kinetic energy, m is the mass of the object, and v is the velocity of the object.
We are given the kinetic energy (KE) and velocity (v), so we can rearrange the formula to solve for the mass (m):
m = 2 * KE / v^2
Substituting the given values, we get:
m = 2 * 390 J / (12 m/s)^2
m = 2 * 390 J / 144 m^2/s^2
m = 5.42 kg (rounded to two decimal places)
Therefore, the mass of the stone is approximately 5.42 kg.