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The slope of the tangent line to this curve at t ! 0 equals the initial velocity v xi , and the slope of the tangent line at any later time t equals the velocity v xf at that time. Finally, we can obtain an expression for the final velocity that does not contain time as a variable by substituting the value of t from Equation 2.9 into Equation (2.13) This equation provides the final velocity in terms of the acceleration and the displace- For motion at zero acceleration, we see from Equations 2.9 and 2.12 that v xf ! v xi ! v x when a x ! 0 x f ! x i % v x t That is, when the acceleration of a particle is zero, its velocity is constant and its posi- v 2 xf ! v 2 xi % 2a x (x f # x i )
(for constant a x ) x f ! x i % 1 2 (v xi % v xf ) " v xf # v xi a x # ! v 2 xf # v 2 xi 2a x t v x (a) t a x (d) t v x (b) t a x (e) t v x (c) t a x (f) Active Figure 2.11 (Quick Quiz 2.5) Parts (a), (b), and (c) are v x -t graphs of objects in one- dimensional motion. The possible accelerations of each object as a function of time are shown in scrambled order in (d), (e), and (f). Quick Quiz 2.5 In Figure 2.11, match each v x -t graph on the left with the a x -t graph on the right that best describes the motion. S E C T I O N 2 . 5 • One-Dimensional Motion with Constant Acceleration 37 Velocity as a function of position } Equations 2.9 through 2.13 are kinematic equations that may be used to solve any problem involving one-dimensional motion at constant acceleration. Keep At the Active Figures link at http://www.pse6.com, you can practice matching appropriate velocity vs. time graphs and acceleration vs. time graphs. |