# 09Lecture_7 - Lecture 7 Feb 2, 2009 Relative Motion Recap...

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Unformatted text preview: Lecture 7 Feb 2, 2009 Relative Motion Recap reference frames Examples An animation of planes in relative motion Forces What is a Force How does it affect motion Newtons first and second laws 1 Reference Frame 2 3 A typical relative motion problem 4 Plane is moving north in the frame of the air. V p,a is the velocity of the plane with respect to the air 5 But the air is moving east (wind!) in the frame of the ground. V ag is the velocity of the air with respect to the ground 6 Speeds v pa = 40 mph v ag = 30 mph v pg = 50 mph Direction = sin-1 (30/50) = 37 0 E of N Example: crossing a river by boat V bw is the velocity of the boat with respect to the water V ws is the velocity of the water with respect to the shore V bs = V bw + V ws is the velocity of the boat with respect to the shore V bs V bw V ws 7 Toy Tractor Questions The table is moving to the left Which direction should I point the toy tractor to get it across the table fastest? A) Angled to the left B) Straight across C) Angled to the right The table is stationary Which direction should I point the toy tractor to get it across the table fastest? A) Angled to the left B) Straight across C) Angled to the right 8 Toy Tractor Answers (B) in both cases. Relative to the table, straight across is the shortest way and thus fastest. However, in the second case (moving table), the truck will end up to the left of its starting point, relative to the ground. 9 Equivalent Question You want to swim across a 50 m wide river in which the current moves at 1.0 m/s with respect to the shore. Your swimming speed is 2.0 m/s with respect to the water....
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## This note was uploaded on 02/25/2009 for the course PHYS 1112 taught by Professor Leclair,a during the Spring '07 term at Cornell University (Engineering School).

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09Lecture_7 - Lecture 7 Feb 2, 2009 Relative Motion Recap...

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