advertisement

Physics Lab – Thursday 12/16/04 – Pick-up materials on front desks – Intro to Horizontal Motion Lab – Bring physics HW to do in class Agenda Physics Agenda Thursday 12/16/04 – Return Plane Labs – Horizontal Motion – HW: Read p. 155-157 and probs. p. 170 #8, 9, 22 Projectile Motion A projectile can be anything that moves though the air after it has been given an initial “thrust” or input force Projectiles are only under one force as they move through the air –GRAVITY! We ignore air resistance in most cases to simply the problems There are two general categories – Projectiles launched horizontally – Projectiles launched at an angle Projectile Motion Bullet Demonstration Ballistics Cart Demo Important Concepts 1. Vertical and horizontal motions are independent of each other 2. We can relate the height, time in the air, and initial vertical velocity of the projectile by using its vertical motion, then determine the range (x-distance) 3. We use basic motion equations to solve! What do You Notice?? Projectiles Launched Horizontally A cat is tossed horizontally at 20 m/s off a cliff that is 50 m high. a) How long is the cat in the air? b) How far from the base of the cliff does the cat land? c) How fast is the cat moving the Instant before it splats on the ground? Problems Solving Strategy 1. Write known and unknown variables 2. Write variables for x and y directions What’s missing? vyf = ? yi = 0 vyi = 0 vxi = 20 m/s ay = g = -9.8m/s2 ax = 0 WHY? vxf = 20 m/s vnetf = ? yf = -50 m xi = 0 t=? xf = ? Practice Problem #2 A plane that is moving 200 m/s drops a package. The package takes 15 seconds to reach the ground. – A) What height was the package dropped from? – B) How far did the plane travel from the time the package was released until the package hit the ground? Is this the same distance the package travels? – C) How fast was the package moving when it hit the ground? End Regents Physics Agenda – Projectile Motion: – Projectiles at any angle HW: problems p. 160 #12,13 problems p. 172 #42, 47 (tricky) Review Problem A plane that is moving 225 m/s drops a package. The package takes 10 seconds to reach the ground. – A) What height was the package dropped from? – B) What horizontal distance did the package cover after it was dropped from the plane? – C) How fast was the package moving when it hit the ground? Projectiles at Any Angle..a few differences When projectiles are launched at any angle, the initial velocity has both horizontal and vertical components This means that Vxi … we’ve Vxi = Vocos Vyi = Vosin Vo must be used, not just done this before! Variables of Motion Other differences and similarities Time in air is called flight time and ½ of flight time occurs at ½ range So..it takes the same amount of time to go up as it does to fall down At ymax, Vyf = 0m/s Still, only force acting on the is gravity Still, no acceleration in the x direction! Practice Problem A football is thrown with an initial velocity of 5.5 m/s at an angle of 49 above the horizontal. 1. How long did it take the ball to return to the launching height? 2. What was the maximum height the ball attained? 3. What was its range? Vyf = 0 m/s Max height range Let’s Play Golf Regents Physics Agenda Review HW Problems and Lab Circular Motion HW: Read p. 163-168 Problems p. 166 #14-16 Circular Motion Question: Can an object be accelerated if its speed remains constant? What’s uniform circular motion? It is the movement of an object or point mass at constant speed around a circle with a fixed radius Circular Motion Demo