A book is lifted upward a vertical distance of 0.800 m. Duringthis displacement, does the gravitational force acting on the book do positivework or negative work? Does the gravitational potential energy of thebook increase or decrease?

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Carleigh Shaffer · Accepted Answer

Step 1The gravitational force and gravitational potential energy depends on the mass of an object and the distance between them.The gravitational force is a force of attraction between the two bodies. The work done by this force on an object can be positive, negative or zero, depending upon the direction of displacement of the object with respect to the forceFormula to calculate work done is,  W  =  F  d  cos  ⁡  θHere, the book is lifted up that is displacement is in upward direction and the gravitational force on the book is in downward direction. Since both force and displacement vector are in opposite direction that is angle (θ ) between them is  Therefore, work done by the gravitational force on the book is negative.Equation of potential energy is,U = mgyAs the work is done against the gravity thus potential energy of the given body will increase by 0.8 mg.

encamineu2cki · Accepted Answer

Step 2(b)In this case,The can falls down that is displacement of can is in downward direction and the gravitational force on the book is also in downward direction. Since both force and displacement vector are in same direction that is angle is in between   0  ≤  θ  ≤      90          ∘      . Thus the work done by the gravitational force on the can is positive.As the work is done in the direction of gravity the potential energy of the given body will decrease by 2 mg .

A book is lifted upward a vertical distance of 0.800

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