Because the act of braking is an example of negative acceleration.
Example: if the rate of braking was say 2 meters per second^2, and the starting velocity was 10 m/s, it would take 5 seconds to come to a stop(during those 5 seconds you would still be moving).
For Mass
K.E = (1/2*mv^2)
Explanation:
Kinetic energy (KE) is equal to half of an object's mass (1/2*m) multiplied by the velocity squared. For example, if a an object with a mass of 10 kg (m = 10 kg) is moving at a velocity of 5 meters per second (v = 5 m/s), the kinetic energy is equal to 125 Joules, or (1/2 * 10 kg) * 5 m/s2.
As an object falls from rest, its gravitational energy is converted to kinetic energy
G.P.E = K.E = mgh
K.E = (80 Kg)(9.8 m/s²)(30 m)
K.E. = 23,520 J
