# Chapter 9 - Work and Kinetic Energy - Exercises and Problems - Page 228: 14

(a) $A\cdot B = 11.5$ (b) $C\cdot D = -4.6$ (c) $E\cdot F = 0$

#### Work Step by Step

(a) $A\cdot B = \vert {A}\vert ~\vert {B}\vert~cos(\theta)$ $A\cdot B = (3)(5)~cos(40^{\circ})$ $A\cdot B = 11.5$ (b) $C\cdot D = \vert {C}\vert ~\vert {D}\vert~cos(\theta)$ $C\cdot D = (2)(3)~cos(140^{\circ})$ $C\cdot D = -4.6$ (c) $E\cdot F = \vert {E}\vert ~\vert {F}\vert~cos(\theta)$ $E\cdot F = (3)(4)~cos(90^{\circ})$ $E\cdot F = (3)(4)(0)$ $E\cdot F = 0$

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