Question

You can find the kinetic energy of a book of a certain mass just before it hits the floor after falling a certain distance by using which equation?

Answer 1

The final kinetic energy is given by $mgh$

Explanation:

The problem can be solved by using the law of conservation of energy: in fact, the total mechanical energy of the book before the fall and after is constant, therefore we can write

$U_i +K_i = U_f + K_f$

where

$U_i$ is the initial potential energy, at the top

$K_i$ is the initial kinetic energy, at the top

$U_f$ is the final potential energy, at the bottom

$K_f$ is the final kinetic energy, at the bottom

We also have that:

$K_i = 0$, assuming that the book starts from rest

$U_f = 0$, assuming the ground as reference level

Therefore the equation becomes

$K_f = U_i$

The initial potential energy can be written as

$U_i = mgh$

where

m is the mass of the book

g is the acceleration of gravity

h is the initial height

And therefore, the final kinetic energy is given by

$K_f = mgh$

Learn more about kinetic energy:

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