Physics 218, Lecture VI 1

Physics 218Lecture 6

Dr. David Toback

Physics 218, Lecture VI 2

Chapter 3, continued

Kinematics in Two or Three Dimensions

• Problems

Physics 218, Lecture VI 3

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Projectile Motion

• 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

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Important Definition ;-)

Word: Defenestration

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

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Push BEVO out of a windowReveille pushes BEVO directly out of a window a height h above the ground. Two Aggies observe that BEVO hits the ground a distance D from the base of the cliff. Assuming BEVO was moving horizontally at the top (and ignoring air friction), how fast must Reveille have pushed her?

h

Dy=0

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Kick a football

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

a) The maximum heightb) The velocity at the maximum heightc) The time of travel before the football hits the

groundd) How far away it hits the grounde) What angle maximizes the distance traveled

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

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Winner: Not my

job award

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More Realistic PuntA football is kicked at angle 0 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?

h

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Rescue Plane

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 height 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?

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Next Week

New Material: Not on the 1st exam• Chapter 4: Read for Next time

–Newton’s Laws of Motion–Reading Questions: 4.7 and 4.16

• Due Tuesday at the beginning of class!– HW2 due Monday

• Cover HW3 in recitation, due the following Monday

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Physics 218, Lecture VI 13

Firing up in the air at an angleA ball is fired up in the air with velocity Vo and angle o. Ignore air friction. The acceleration due to gravity is g pointing down.What is the final velocity here?

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Rescue Plane

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:

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

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Rescue Plane cont.

b) 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.

c) What is the speed of the supplies as they hit the ground?

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Announcements: Exam 1

• 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.

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Next Week• 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)

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Example: 3-8

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