Question

A student lifts a set of books off a table and places them in the upper shelf of a book case which is 2 meters above the table. If she applies a force of 5 newtons to lift these books, what is the work done?
0 joules
2.5 joules
-2.5 joules
10 joules
-10 joules

Answer 1

Answer:

D.10 joules

Explanation:

Answer 2

The work done is the product between the intensity of the force applied F, the amount of the displacement d of the book and the cosine of the angle $\theta$ between the direction of the force and the direction of the displacement:
$W=Fd \cos \theta$
In our problem, the student is lifting the book, so he is applying a force directed upward, and the book is moving upward, so F and d are parallel and therefore the angle is zero, so $\cos \theta = \cos 0=1$
Therefore, the work done is
$W=Fd=(5 N)(2 m)=10 J$