The initial kinetic energy of a block moving on a horizontal floor is 48 J. A constant frictional force acts on the block bringing it torest over a distance of 2 m. What is the frictional force on the block?
Question
The initial kinetic energy of a block moving on a horizontal floor is 48 J. A constant frictional force acts on the block bringing it torest over a distance of 2 m. What is the frictional force on the block?
Solution
Para resolver este problema, utilizaremos el principio de trabajo y energía. El trabajo realizado por la fuerza de fricción es igual al cambio en la energía cinética del bloque.
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La energía cinética inicial del bloque es 48 J.
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La energía cinética final del bloque es 0 J, ya que se detiene.
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El cambio en la energía cinética es:
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El trabajo realizado por la fuerza de fricción es igual al cambio en la energía cinética:
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El trabajo realizado por la fuerza de fricción también se puede expresar como: Donde:
- es la fuerza de fricción.
- es la distancia sobre la cual actúa la fuerza de fricción, que es 2 m.
- es el ángulo entre la fuerza de fricción y la dirección del movimiento. En este caso, porque la fuerza de fricción actúa en la dirección opuesta al movimiento, y .
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Sustituyendo los valores, tenemos:
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Simplificando, obtenemos:
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Dividiendo ambos lados por -2 m, obtenemos:
Por lo tanto, la fuerza de fricción que actúa sobre el bloque es de 24 N.
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