Explain what happens to the kinetic energy of a skateboard that is coasting along a flat surface, slows down, and comes to a stop.

When the skateboard slides over a flat surface, there is a frictional force between the skateboard's wheels and the surface. This frictional force transforms kinetic energy into thermal energy as the skateboard loses speed until the skateboard stops.

Explanation:

Kinetic energy is the form of energy that any body has as a result of its movement, in other words, it is the form of energy associated with the speed of a body. When we apply a resultant nonzero force to some body, we are doing work on it, so that it acquires kinetic energy as its velocity increases.

The kinetic energy of a body can be decreased in two cases: when it is stored in the form of potential, elastic or gravitational energy, for example; or when there are dissipative forces that can transform it into other forms of energy, as does the frictional force that transforms kinetic energy into thermal energy. Therefore, unless there are no dissipative forces, the body's kinetic energy can always return to its initial modulus, since in this case it will be converted into potential energy without loss.

In the case of the skateboard shown above, there is a frictional force that causes the skateboard to lose speed. This friction turns kinetic energy into thermal energy. As the kinetic energy decreases, the speed of the skateboard decreases until it stops moving.

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.

d. cellulose and starch