midterm_examA_F08_solutions

Midterm_examA_F08_so - Physics 40A Midterm Exam Solutions Fall 2008 Exam A Problem 1[25 points You throw a ball with a speed of 25 m/s at an angle

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Physics 40A - Midterm Exam Solutions - Fall 2008 - Exam A Problem 1 [25 points] You throw a ball with a speed of 25 m/s at an angle of 40° above the horizontal directly toward a wall (see Figure). The wall is 22 m from the release point of the ball. (a) How long does the ball take to reach the wall? (b) How far above the release point does the ball hit the wall? (c) What are the horizontal and vertical components of its velocity as it hits the wall? (d) When it hits, has it passed the highest point on its trajectory? Explain your reasoning. Solution: This is a projectile motion problem so the horizontal acceleration is zero and the vertical acceleration is g . We define the origin of our coordinate system at the release point with + y vertically upward and + x horizontal (toward the wall). The x and y components of the initial velocity are v 0x = v 0 cos 0 = 25 m/s  cos 40 ° = 19.2 m/s v 0y = v 0 sin 0 25 m/s sin 40 ° 16.1 m/s (a) To find the time at which the projectile hits the wall ( x = 22 m) we can use x x 0 = v 0x t The horizontal displacement of the ball is x x 0 = 22 m, so we obtain t = x x 0 v 0x = 22 m 19.2 m/s t = 1.15s (b) The vertical distance is y y 0 = v 0y t 1 2 gt 2 16.1 m/s 1.15 s − 1 2 9.8 m/s 2 1.15 s 2 y y 0 = 12.0 m

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This note was uploaded on 04/16/2008 for the course PHYS 40 taught by Professor Ellison during the Winter '08 term at UC Riverside.

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Midterm_examA_F08_so - Physics 40A Midterm Exam Solutions Fall 2008 Exam A Problem 1[25 points You throw a ball with a speed of 25 m/s at an angle

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