Question

What kind of energy transformation occurs when a body falls from a certain height?
A. Kinetic to potential energy
B. Potential to Kinetic energy
C. Potential to heat energy
D. Potential to chemical energy

Answer 1

Hint: In order to solve this question we need to understand mechanical energy conservation which states that if the force is conservative in nature then the rate of decrease of potential energy would be equal to rate of increase of kinetic energy and vice versa. Conservative means that potential is independent of time and it only depends on the space coordinate so the work done along a circle would be zero, for example that potential energy in an electric field is time independent. Why work done along a circle is zero consequence of this is that electric fields do not exist in curved nature.

Complete step by step answer:
Consider a body at some height, say $h$. We know acceleration is only in downward directions due to gravity, so acceleration is equal to $g$. Let the mass of the body be, $m$.So potential energy is given by, $U = mgh$. Now the body starts to fall vertically downward then since the mechanical work done by mechanical force is zero so whole of potential energy would be converted to kinetic energy.

Let the speed of the body while falling near to ground be, $v$. Then kinetic energy is given by,
$K = \dfrac{1}{2}m{v^2}$
So, $U = K$ because at the time of falling from height whole potential energy will convert into Kinetic energy according to the law of conservation of energy.
$mgh = \dfrac{1}{2}m{v^2}$
So, we see that whole potential energy gets converted into Kinetic energy during the falling of a body from a certain height.

Hence, correct option is B.

Note: It should be remembered that we have neglected air resistance so there would be no dissipation of heat while falling however this is ideal case whereas in real case there would be dissipation in heat as air resistance would act so whole kinetic energy would not be equal to potential energy. Energy can never be destroyed nor can it be created.