Kinetic energy is defined as the energy possessed by the body due to its motion.

Formula

Kinetic energy is mathematically defined by the formula:

K.E = 1/2mv2

Examples

Example#1: A 0.2 kg stone hits the ground with a velocity of 10 m/s. Find the kinetic energy of stone at the instant it hits the ground?

Solution: K.E = 1/2 (0.2 kg) * (10 m/s)2

K.E = 1/2 * 0.2 kg * 100 m2/s2

K.E = 1/2 * 0.2 kg * 100 m2/s2

K.E = 10 J


If mass is given in grams, first g to kg conversion is needed. Let’s solve an example.

Example#2: A block weighing 800 grams hits the ground with a velocity of 25 m/s. Find the kinetic energy of stone at the instant it hits the ground.

Solution: mass = 800 g = 0.8 kg

K.E = 1/2 (0.8 kg) * (25 m/s)2

K.E = 1/2 * 0.8 kg * 625 m2/s2

K.E = 250 J