Suppose one's hand exerts a force of 12 N upward on a book weighing 10 N. The reaction to the force of the hand on the book is a force of O 12 N exerted by the book on the hand. 2 N exerted by the book on the hand. O 10 N exerted by the book on the hand. O 10 N exerted by the book on the Earth. O 10 N exerted by the Earth on the book. Suppose you climb the stairs of an eight-story building, about 24 m high, and your mass is 70 kg. The gravitational potential energy you gain is about O 40 Joule. O40 calories. O 16,500 Joule. 16,500 calories.