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# Physics 218 - PowerPoint PPT Presentation

Physics 218 Lecture 6 Dr. David Toback Chapter 4, continued Kinematics in Two Dimensions Today  Problems Projectile Motion The physics of the universe: The horizontal and vertical Equations of Motion behave independently This is why we use vectors in the first place Projectile Motion

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### Physics 218Lecture 6

Dr. David Toback

Physics 218, Lecture VI

Kinematics in Two Dimensions

TodayProblems

Physics 218, Lecture VI

The physics of the universe:

The horizontal and vertical Equations of Motion behave independently

This is why we use vectors in the first place

Physics 218, Lecture VI

• This is the heart and culmination of what we have learned so far

• You can rest assured there will be a problem like one in lecture today on the exam

Physics 218, Lecture VI

• Next we’ll do an example problem like one of the homework problems in the text book

• Solve this problem using the right method

• Draw a diagram

• Convert the numbers to variables

• Solve to get a formula

• Plug in the numbers at the end

• Check

• Reasonable numbers?

• Silly numbers?

• Another way to do the same problem?

Physics 218, Lecture VI

The trick for all these problems is to

break them up into the X and Y directions

Physics 218, Lecture VI

A ball is fired up in the air with speed Vo and angle Qo. Ignore air friction. The acceleration due to gravity is g pointing down.

What is the final velocity here?

Physics 218, Lecture VI

Word: Defenestration

Definition: The act of throwing someone or something out of a window

Physics 218, Lecture VI

Reveille pushes BEVO directly out of a window that is a height h above the ground. Two Aggies observe that BEVO hits the ground a distance D from the base of the building.

Assuming BEVO was moving horizontally at the top (and ignoring air friction), how fast must Reveille have pushed her?

h

y=0

D

Physics 218, Lecture VI

A football is kicked at angle Q with respect to the ground with speed V0. Calculate:

• The maximum height

• The velocity at the maximum height

• The time of travel before the football hits the ground

• How far away it hits the ground

• What angle maximizes the distance traveled

Assume the ball leaves the foot at ground level and ignore air resistance

Physics 218, Lecture VI

Winner: Not my job award

Physics 218, Lecture VI

h

A football is kicked at angle Q0 with a speed V0. The ball leaves the punters foot h meters above the ground.

How far does it travel, in the X direction, before it hits the ground?

Physics 218, Lecture VI

You are the pilot of a rescue plane and you are flying a plane with a horizontal speed of Vp. Your mission is to drop supplies for some mountain climbers on a ridge a vertical distance h below.

To do this you have to release the supplies a horizontal distance R in advance of the mountain climbers.

What vertical velocity should you give the supplies so that they arrive precisely at the the climbers position?

Physics 218, Lecture VI

New Material: Not on the 1st exam

• Chapter 5:Read for Next time

• Newton’s Laws of Motion

• HW2 due Monday

• Cover CH. 3&4 in recitation, due the following Monday

• Lab 3 (posted on the website)

Physics 218, Lecture VI

Physics 218, Lecture VI

• Homework:

• HW1 was due yesterday

• HW2 covered in recitation this week; due this coming Monday

• Start working on HW for Chap 3 & 4

• Next time: More on kinematics in two dimensions

Physics 218, Lecture VI

Analyze Vertical and Horizontal separately!!!

• Ay = g (downwards)

• Ax = 0

• Constant for Both cases!!!

Vx = 0

Vx>0

Physics 218, Lecture VI

Prove that an object projected horizontally will reach the ground at the same time as an object dropped vertically

Physics 218, Lecture VI

A ball is fired up in the air with velocity Vo and angle Qo. Ignore air friction. The acceleration due to gravity is g pointing down.

What is the final velocity here?

Physics 218, Lecture VI

You are the pilot of a rescue plane. Your mission is to drop supplies to isolated mountain climbers on a rocky ridge a height h below. If your plane is traveling horizontally with a speed of VO:

• How far in advance of the recipients (horizontal distance) must the goods be dropped?

Physics 218, Lecture VI

• Suppose instead, that your plane can’t get to that position. Instead you must release the supplies a horizontal distance D in advance of the mountain climbers. What vertical velocity should you give the supplies so that they arrive precisely at the the climbers position.

• What is the speed of the supplies as they hit the ground?

Physics 218, Lecture VI

• We will move the date of Exam 1 from Tuesday Feb 11th.

• Next week you need to do the reading for Chapter 4, Chapter 3-9 and Chapter 5. There will be quizzes on both.

• Note: You will get recitation on Chapter 3 and turn in your Homework before the exam.

Physics 218, Lecture VI

• Chapter 4: (NOT ON 1st EXAM)

• Dynamics

• Newton’s Laws of Motion

• Finish HW3. Labs & Rec/Web as usual

• Exam Thursday: Here during regular time

• Bring a calculator and ruler

• Formula sheet will be provided (on the web already)

• Will cover:

• Chapter 1 (1-6)

• Calculus 1

• Chapter 2 (1-7)

• Chapter 3 (1-8, 10)

Physics 218, Lecture VI

Derive a formula for the horizontal range, R, of a projectile in terms of its initial velocity (v0 & Q) before the projectile travels before returning to its original height

Physics 218, Lecture VI