Suppose you slowly, and at constant speed, lift a book weighing 12 N from the floor to a shelf 2 m above the floor. Neglect air resistance. While you are lifting, the net force on the book is
A) less than 12 N, by an amount that depends on the speed of lifting.
B) more than 12 N, by an amount that depends on the speed of lifting.
C) 12 N directed upward.
D) zero.
E) 12 N directed downward.
D
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