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# Physics Lesson 6 Projectile Motion

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Physics Lesson 6 Projectile Motion
Eleanor Roosevelt High School Mr. Chin-Sung Lin

Introduction to Projectile Motion
What is Projectile Motion? Trajectory of a Projectile Calculation of Projectile Motion

Introduction to Projectile Motion
What is Projectile Motion? Trajectory of a Projectile Calculation of Projectile Motion

What is Projectile Motion?

Features of Projectile Motion?
Thrown into the Air 2-D Motion Parabolic Path Affected by Gravity Determined by Initial Velocity

Definition: Projectile Motion
Projectile motion refers to the 2-D motion of an object that is given an initial velocity and projected into the air at an angle. The only force acting upon the object is gravity. It follows a parabolic path determined by the effect of the initial velocity and gravitational acceleration.

Definition: Projectile Motion
Projectile motion refers to the 2-D motion of an object that is given an initial velocity and projected into the air at an angle. The only force acting upon the object is gravity. It follows a parabolic path determined by the effect of the initial velocity and gravitational acceleration. 7

Introduction to Projectile Motion
What is Projectile Motion? Trajectory of a Projectile Calculation of Projectile Motion

Trajectory (Path) of a Projectile

Trajectory (Path) of a Projectile

y v0 x

y x

y x

y x

g = -9.81m/s2 y x Velocity is changing and the motion is accelerated
The horizontal component of velocity (vx) is constant Acceleration from the vertical component of velocity (vy) Acceleration due to gravity is constant, and downward a = g = m/s2 g = -9.81m/s2 x

y The horizontal and vertical motions are independent of each other Both motions share the same time (t) The horizontal velocity vx = v0 The horizontal distance .... dx = vx t The vertical velocity vy = g t The vertical distance dy = 1/2 g t2 g = -9.81m/s2 x

Trajectory (Path) of a Projectile
The path of a projectile is the result of the simultaneous effect of the H & V components of its motion H component  constant velocity motion V component  accelerated downward motion H & V motions are independent H & V motions share the same time t The projectile flight time t is determined by the V component of its motion

Horizontally Launched Projectile
H velocity is constant vx = v0 V velocity is changing vy = g t H range: dx = v0 t V distance: dy = 1/2 g t2

Introduction to Projectile Motion
What is Projectile Motion? Trajectory of a Projectile Calculation of Projectile Motion

Calculation of Projectile Motion
Example: A projectile was fired with initial velocity v0 horizontally from a cliff d meters above the ground. Calculate the horizontal range R of the projectile. g R d v0 t

Strategies of Solving Projectile Problems
H & V motions can be calculated independently H & V kinematics equations share the same variable t g R d v0 t

Strategies of Solving Projectile Problems
H motion: dx = vx t R = v0 t V motion: dy = d = 1/2 g t t = sqrt(2d/g) So, R = v0 t = v0 * sqrt(2d/g) g R d v0 t

Numerical Example of Projectile Motion
H motion: dx = vx t R = v0 t = 10 t V motion: dy = d = 1/2 g t t = sqrt(2 *19.62/9.81) = 2 s So, R = v0 t = v0 * sqrt(2d/g) = 10 * 2 = 20 m V0 = 10 m/s g = 9.81 m/s2 19.62 m t R

Exercise 1: Projectile Problem
A projectile was fired with initial velocity 10 m/s horizontally from a cliff. If the horizontal range of the projectile is 20 m, calculate the height d of the cliff. g = 9.81 m/s2 20 m d V0 = 10 m/s t

Exercise 1: Projectile Problem
H motion: dx = vx t = v0 t = 10 t t = 2 s V motion: dy = d = 1/2 g t2 = 1/2 (9.81) 22 = m So, d = m g = 9.81 m/s2 20 m d V0 = 10 m/s t

Exercise 2: Projectile Problem
A projectile was fired horizontally from a cliff m above the ground. If the horizontal range of the projectile is 20 m, calculate the initial velocity v0 of the projectile. g = 9.81 m/s2 20 m 19.62 m V0 t

Exercise 2: Projectile Problem
H motion: dx = vx t = v0 t V motion: dy = d = 1/2 g t t = sqrt(2 *19.62/9.81) = 2 s So, = v0 t = 2 v v0 = 20/2 = 10 m/s g = 9.81 m/s2 20 m 19.62 m V0 t

Summary of Projectile Motion
What is Projectile Motion? Trajectory of a Projectile Calculation of Projectile Motion

V & H Velocity Vectors of Projectile

Launch Angles of Projectile

Projectile Motion with Angles

Example: Projectile Problem – H & V
A projectile was fired from ground with 20 m/s initial velocity at 60-degree angle. What’s the horizontal and vertical components of the initial velocity? g = 9.81 m/s2 20 m/s vy 60o vx

Example: Projectile Problem – At the Top
A projectile was fired from ground with 20 m/s initial velocity at 60-degree angle. What’s the velocity of the projectile at the top of its trajectory? v g = 9.81 m/s2 20 m/s vy t 60o vx R

Example: Projectile Problem – Height
A projectile was fired from ground with 20 m/s initial velocity at 60-degree angle. What’s the maximum height that the ball can reach? g = 9.81 m/s2 20 m/s vy h 60o vx

Example: Projectile Problem - Time
A projectile was fired from ground with 20 m/s initial velocity at 60-degree angle. How long will the ball travel before hitting the ground? g = 9.81 m/s2 20 m/s vy t 60o vx

Example: Projectile Problem – H Range
A projectile was fired from ground with 20 m/s initial velocity at 60-degree angle. How far will the ball reach horizontally? g = 9.81 m/s2 20 m/s vy 60o vx R

Example: Projectile Problem – Final V
A projectile was fired from ground with 20 m/s initial velocity at 60-degree angle. What’s the final velocity of the projectile right before hitting the ground? g = 9.81 m/s2 20 m/s vy 60o vfx vx vfy vf

Example: Projectile Problem – Max R
A projectile was fired from ground with 20 m/s initial velocity. How can the projectile reach the maximum horizontal range? What’s the maximum horizontal range it can reach? g = 9.81 m/s2 20 m/s q R

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