14) A machine puts out 100 watts of power for every 1000 watts put into it. The effici of the machine is A) 10%. B) 50%. C) 90%. D) 110%. 15) A jack system will increase the potential energy of a heavy load by 1000 J with a v input of 2000 J. The efficiency of the jack system is A) 10%. B) 20%. C) 50%. D) 80%. 16) If the Sun were twice as massive A) its pull on Earth would double. B) the pull of Earth on the Sun would double. C) both of these D) neither of these 17) The force of Earth's gravity on a capsule in space increases as it comes closer. W the capsule moves to half its distance, the force toward Earth is then A) twice. B) three times greater. C) four times greater. D) none of the above 18) The element gold contains A) gold atoms. B) atoms that combine to produce gold. C) gold atoms plus various slightly lighter and heavier atoms. D) none of the above 19) Which of the following are electrically neutral? A) protons B) neutrons C) electrons D) ions 20) Which is the lightest particle? A) proton B) electron C) neutron D) all about the same 21) An element is distinct because of its number of A) protons. B) neutrons. C) electrons. D) the total mass of all the particles. 22) The number of protons in a neutral atom is balanced by an equal number of A) electron shells that surround the nucleus. B) neutrons in the nucleus. C) orbital electrons. D) none of the above 23) An isotope is simply an atom that A) is electrically charged. B) has different numbers of neutrons for the same element. C) both of these D) neither of these 24) Although solid matter is mostly empty space, we don't fall through the floor because A) atoms are constantly vibrating, even at absolute zero. B) of nuclear forces. C) of gravitational forces. D) of electrical forces. 25) The bob of a simple pendulum has its maximum potential energy at the A) top of its swing. B) bottom of its swing. C) midpoint between top and bottom. D) at all points along its path of swing.