A calculus book weighing 20 N rests on the floor of a classroom. The reaction to the force of the floor on the book is a force of
A. 9.8 m/s2 exerted by the Earth on the book.
B. 2.04 kg exerted by the floor on the book.
C. 20 N exerted by the book on the Earth.
D. 0 N.
E. 20 N exerted by the book on the floor.
Answer: C
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