According to the law of reflection, which statement must be true?

100 joules

Explanation:

Given that

Mass of rock = 0.5-kg

Velocity = 20 m/s

Kinetic energy = ?

Kinetic energy is the energy possessed by a moving object, and it depends on its mass and velocity.

Thus, K.E = 1/2 x Mass x (velocity)^2

K.E = 1/2 x 0.5kg x (20m/s)^2

K.E = 0.5 x 0.5 x 400

K.E = 100 J

Thus, the kinetic energy of the rock is 100 joules.