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S E C T I O N 4 . 3 • Projectile Motion 85 (1) constant-velocity motion in the horizontal direction and (2) free-fall motion in the vertical direction. The horizontal and vertical components of a projectile’s Quick Quiz 4.3 Suppose you are running at constant velocity and you wish to throw a ball such that you will catch it as it comes back down. In what direction Quick Quiz 4.4 As a projectile thrown upward moves in its parabolic path (such as in Figure 4.8), at what point along its path are the velocity and acceleration Quick Quiz 4.5 As the projectile in Quick Quiz 4.4 moves along its path, at what point are the velocity and acceleration vectors for the projectile parallel to each Example 4.2 Approximating Projectile Motion A ball is thrown in such a way that its initial vertical and hor- Solution A motion diagram like Figure 4.9 helps us concep- 2 . The velocity vectors change direc- tion. Their horizontal components are all the same: 20 m/s. Remember that the two velocity components are inde- pendent of each other. By considering the vertical motion Figure 4.9 (Example 4.2) Motion diagram for a projectile. r f x (x, y) gt 2 v i t O y 1 2 Figure 4.8 The position vector r f of a projectile launched from the origin whose initial velocity at the origin is v i . The vector v i t would be the displacement of the projectile if gravity were absent, and the vector is its vertical displacement due to its downward gravitational acceleration. 1 2
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