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Lesson 2: Energy

# Kinetic energy derivation

Let's derive the K.E. expression 1/2 m v^2.   Created by Mahesh Shenoy.

## Want to join the conversation?

• If kinetic energy = work = Fs then why don't we just use Fs for calculating kinetic energy? Is it because the expression does not involve mass and velocity? Can someone clarify this for me?
• Why does the ball move in the opposite direction to the force applied by the hand?
(1 vote)
• Newtons 3rd law states that there is an equal and opposite reaction so it goes in the opposite direction
• Can someone explain this V0 part?
(1 vote)
• Here, v stands for the final velocity during the motion, which, in the case of the ball is 0 since it finally comes to a state of rest.
(1 vote)
• So basically, if a ball has 10 joules of kinetic energy and hits me, I will feel 10J of force right?
(1 vote)
• here you cancel the negative sign, but a square number can never be negative, so how did you cancel it ??
(1 vote)
• Dear Khan team, to use this movement equation is necessary to assume a constant accelaration doesn´t it?
(1 vote)
• how can this equation be used everywhere, for it the final velocity must be zero then only we will end up with that equation?
(1 vote)
• What are the equations of motion and how to read these three equations of motion?
• The three equations are,

v = u + at
v² = u² + 2as
s = ut + ½at²

where: s = displacement; u = initial velocity; v = final velocity; a = acceleration; t = time of motion.