Question

A child is sliding down a slide at the playground.


Is the mechanical energy conserved? Why or why not?



The mechanical energy is conserved. There is as much KE at the end as there was PE at the beginning.



Mechanical energy is always conserved.



The mechanical energy isn't conserved. Some energy is lost to gravity.



The mechanical energy isn't conserved. Some energy is lost to friction.

please help!

Answer 1

Answer:

The mechanical energy isn't conserved. Some energy is lost to friction.

Explanation:

The mechanical energy of an object is the sum of the potential energy (PE) and the kinetic energy (KE) of the object:

$E=PE+KE$

where

- The potential energy is the energy due to the position of the object

- The kinetic energy is the energy due to the motion of the object

According to the law of conservation of energy, the total mechanical energy of an object is conserved IF there are no frictional forces acting on it.

However, this is not the case.

In fact, as the child slides down, the friction force between the slide and the child acts on him, slowing him down. As a result, part of the mechanical energy is "lost", converted into thermal energy due to the interaction between the molecules of the slide and of the surface of the child.

Therefore, the correct answer is

The mechanical energy isn't conserved. Some energy is lost to friction.