Which is the best example of the law of conservation of energy?
a) a basketball stops bouncing because its energy disappears.
b) a rolling skateboard slows down because some of its kinetic energy changes to heat.
c)a falling book hits the ground and all of its energy is destroyed.
d)a toy car gains speed as it moves down a ramp because the ramp creates energy.

B) A rolling skateboard slows down because some of its kinetic energy changes to heat.

Explanation:

As we know by the law of conservation of energy that energy neither be created nor it can be destroyed but energy can convert from one form to another form.

So here we can say that in all such examples where energy is converted into one form to other form is an example of energy conservation

so here when we say that rolling skateboard slows down then in that case the kinetic energy of skateboard must have to convert into another form of energy. Since that energy is given in form of heat energy so this is a correct example of energy conservation.

so correct answer will be

B) A rolling skateboard slows down because some of its kinetic energy changes to heat.

t = 1/400 h   ⇔ 0.0025 h ⇔ 9s ⇔ 0.15 m

any of the answers are correct.