# Question #d6576

Nov 21, 2014

Kinetic Energy is the energy of motion. An object in motion has a Kinetic Energy which can be calculated from its mass and velocity.

$K E = \frac{1}{2} m {v}^{2}$

This can also be thought of as the amount of work that was done on the object to get it up to the velocity $v$. Alternatively, it is the amount of work that will be required to slow the object down from velocity $v$ to rest.

A 1000 kg car traveling down the road at 20 $\frac{m}{s}$ as a Kinetic Energy
$K E = \frac{1}{2} \cdot 1000 \cdot {20}^{2} \frac{k g {m}^{2}}{s} ^ 2 = 200 , 000 J$

To bring the car to a stop one needs either a large force for a short period of time (hitting a brick wall) or a small force for a longer period of time (imagine sliding on an icy road). The ideal stoping force and distance are somewhere in between, of course. But the amount of Kinetic Energy which must be converted into another form is the same.