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 isnt conserved. some energy is lost to gravity.
the mechanical energy isnt conserved. some energy is lost to friction.

Explanation:

To determine if mechanical energy is conserved when a child slides down a slide, we analyze the forces involved. When sliding, friction acts between the child and the slide. Mechanical energy (sum of kinetic and potential energy) is conserved only in the absence of non - conservative forces like friction. Friction does work on the child, converting some mechanical energy into thermal energy (heat).

• The first option is wrong because friction causes energy loss, so kinetic energy (KE) at the end won't equal the initial potential energy (PE).
• The second option is wrong as mechanical energy is not always conserved; non - conservative forces (like friction here) can cause energy loss.
• The third option is wrong because gravity is a conservative force and doesn't cause energy loss from the mechanical energy system (it converts PE to KE).
• The fourth option is correct as friction is a non - conservative force that causes mechanical energy to be lost (converted to heat).

Answer:

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