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lana summarized what happens when a ball sitting on top of a grassy hill rolls down the hill.

The motionless ball has potential energy. Once the ball starts to roll down the hill, new kinetic energy is made. As the ball rolls across the grass, it slows down. The kinetic energy of the ball is converted to other forms of energy.

Which best describes Alana’s error?

The motionless ball does not have energy because it is still.
Kinetic energy is not made; it is a result of energy transformation.
The ball cannot slow down unless someone touches it.
The energy is not converted; it disappears.

Respuesta :

Answer:

Kinetic energy is not made; it is a result of energy transformation

Explanation:

Let's discuss what happens to the ball when it is on top of the mountain and rolls down.

Initially the ball has a total mechanical energy, which at this point is potential.

         Em₀ = U = mg h

When the ball starts to roll down, part of this potential energy will be transformed into kinetic energy.

        Em = K + U = ½ m v² + mg y

but mechanical energy is conserved.

The presence of the grass introduces a force in the opposite direction that creates a friction force work (not conservative), for which the total mechanical energy decreases

          W_{friction}= Emf - Emo  

When examining the answers, the one that best describes Lana's error is:

Kinetic energy is not made; it is a result of energy transformation

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