Unit Kinematics Module One Dimensional Motion Under Constant Acceleration page 1 of 1 Solving Problems Involving Motion Under Constant Acceleration The master equations of kinematics with constant acceleration describe the motion of an object in one dimension v f v i a t v f 2 v i 2 2a x x f x i v i t 1 2 a t 2 A race car is driven 25 m in 5 s What is its velocity as it crosses the finish line You need to use the master equations of kinematics The first two equations allow you to solve for vf the final velocity However both of these equations require that you know the car s acceleration a and the value of a is not given in the problem Look at the third equation You know the value of all the terms except for acceleration If you let xi 0 m then xf 25 m The car started at rest so m v i 0 The time required for the trip t was 5 s s You can solve the third equation of kinematics for m the car s acceleration a 2 2 s Substitute the value of the car s acceleration into the first equation of kinematics and solve for the velocity m of the car as it crosses the finish line v f 10 s You can check your answer using the second equation of kinematics Notice that while the instantaneous velocity of the car as it crosses the m finish line is 10 the car s average velocity for the s m x 25 m entire race is v 5 5s s t www thinkwell com info thinkwell com Copyright 2001 Thinkwell Corp All Rights Reserved 1807 rev 06 21 2001
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