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Horizontal Projectile Motion By Lisa Levenson Katya Fatakhova Kaitlin Magee Daniel Wittenberg Horizontal Projectile Motion • An object fired or thrown horizontally • The vertical velocity of the object is always 0. • The object falls to the ground vertically, and maintains an acceleration of 9.81 m/s2 (Like in Free Fall) Break Packet #31-Horizontal Projectile Motion A 0.2-kilogram red ball is thrown horizontally at a speed of 4 meters per second from a height of 3 meters. A 0.4-kilogram green ball is thrown horizontally from the same height at a speed of a 8 meters per second. Compared to the time it takes the red ball to reach the ground, the time it takes the green ball to reach the ground is A) twice as great B) the same C) four times as great D) one-half as great ANSWER!!!! A 0.2-kilogram red ball is thrown horizontally at a speed of 4 meters per second from a height of 3 meters. A 0.4-kilogram green ball is thrown horizontally from the same height at a speed of a 8 meters per second. Compared to the time it takes the red ball to reach the ground, the time it takes the green ball to reach the ground is A) twice as great B) the same C) four times as great D) one-half as great EXPLANATION This problem can be solved through the equation: dy = vi(t)+(1/2)at2 vi = 0, so that part of the equation can be eliminated. t = √(2d/a) Therefore (neglecting air resistance), the only factors that affect the time of the object's fall is its distance from the ground and its acceleration, both of which are the same for the two objects in this problem. A ball is thrown horizontally with an initial velocity of 20 meters per second from the top of a tower 60 meters high. What is the horizontal velocity of the ball just before it reaches the ground? [Neglect air resistance.] (A) 34.3 m/s (B) 20.0 m/s (C) 68.6 m/s (D) 9.81 m/s A ball is thrown horizontally with an initial velocity of 20 meters per second from the top of a tower 60 meters high. What is the horizontal velocity of the ball just before it reaches the ground? [Neglect air resistance.] (A) 34.3 m/s (B) 20.0 m/s (C) 68.6 m/s (D) 9.81 m/s ANSWER EXPLAINED The answer would be equivalent to the initial velocity. The horizontal velocity does not change when the ball is thrown in the air. Neglecting air resistance, there is no horizontal acceleration, and therefore the horizontal velocity remains constant. Newton's First Law: An object in motion tends to stay in motion(at a constant velocity), unless acted upon by an outside force. Review - Short Answer An airplane flying horizontally at 150m/s drops a bomb from a height of 2500m. How far in front of the target must the bomb be released? This problem must be solved in two steps: 1) Find the time it takes for the bomb to hit the ground dy = viy + (1/2)at2 (The initial y velocity is 0.) 2,500m = (1/2)(9.81m/s2)t2 2,500m = 4.9m/s2(t)2 2,500m/4.9m/s2 = t2 t = √(510s2) t = 23s Review - Short Answer (continued) 2) Find the range (using t) dx= vit + (1/2)at2 (In this case velocity is constant, and so there is no acceleration) dx = vit dx=(150m/s)(23s) dx= 3.5 x 103m The bomb must be released 3.5 x 103m in front of the target. ANGRY BIRDS PROJECTILE ANIMATION http://www.youtube.com/watch?v=vfWgzQHX9Fg&feature=re lated In this game, in order to kill the pigs, one must find the proper angle to shoot the "angry birds." This shows projectile motion, and also demonstrates the idea that at different angles, an object has varied flight time, and flight distance. HOMEWORK Homework will be given out on a worksheet in class.