192 Energy and Energy Transfer Q7.10 Kinetic energy is always positive. Mass and squared speed are both positive. A moving object can always do positive work in striking another object and causing it to move along the same direction of motion. Q7.11 Work is only done in accelerating the ball from rest. The work is done over the effective length of the pitcher’s arm—the distance his hand moves through windup and until release. Q7.12 Kinetic energy is proportional to mass. The first bullet has twice as much kinetic energy. Q7.13 The longer barrel will have the higher muzzle speed. Since the accelerating force acts over a longer distance, the change in kinetic energy will be larger. Q7.14 (a) Kinetic energy is proportional to squared speed. Doubling the speed makes an object's kinetic energy four times larger. (b) If the total work on an object is zero in some process, its speed must be the same at the final point as it was at the initial point. Q7.15
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This note was uploaded on 12/14/2011 for the course PHY 203 taught by Professor Staff during the Fall '11 term at Indiana State University .