# HW-CH7 - HW-CH7 9th Edition CH7 Problems 5 21 36 78 8th...

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Unformatted text preview: HW-CH7 9th Edition CH7 Problems: 5, 21, 36, 78 8th Edition CH7 Problems: 5, 19, 34, 80 5. A father racing his son has half the kinetic energy of the son, who has half the mass of the father. The father speeds up by 1.0 m/s and then has the same kinetic energy as the son. What are the original speeds of (a) the father and (b) the son? 21. A cord is used to vertically lower an initially stationary block of mass M at a constant downward acceleration of g=4. When the block has fallen a distance d, ...nd (a) the work done by the cord' force on the block, (b) the s work done by the gravitational force on the block, (c) the kinetic energy of the block, and (d) the speed of the block. 36. A 5.0 kg block moves in a straight line on a horizontal frictionless surface under the in uence of a force that varies with position as shown in Fig. 7-39. The scale of the ...gure' vertical axis is set by Fs = 10:0N . How s much work is done by the force as the block moves from the origin to x = 8:0m? 78. A CD case slides along a oor in the positive direction of an x axis while ~ an applied force Fa acts on the case. The force is directed along the x axis and has the x component Fax = 9x 3x2 , with x in meters and Fax in newtons. The case starts at rest at the position x = 0, and it moves until ~ it is again at rest. (a) Plot the work Fa does on the case as a function of x, (b) At what position is the work maximum, and (c) what is that maximum value? (d) At what position has the work decrease to zero? (e) At what position is the case again at rest? 1 ...
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