Conservation of energy of a marble problem

[Amar.alchemy]

Homework Statement

A uniform marble rolls down a symmetric bowl, starting from rest at the top of the left side. The top of each side is a distance h above the bottom of the bowl. The left half of the bowl is rough enough to cause the marble to roll without slipping, but the right
half has no friction because it is coated with oil. (a) How far up the smooth side will the marble go, measured vertically from the bottom?

Homework Equations

Conservation of energy

The Attempt at a Solution

While applying conservation of energy, why we should not consider the work done by the friction force on the marble? Kindly explain me.

 

[kuruman]

Because the marble rolls without slipping, there is no heat generated at the point of contact so no Joules are lost to friction. For heat to be generated, the two surfaces need to rub against each other.

 

[Amar.alchemy]

ok, Thanks :)