1. PHY 231 1 PHYSICS 231 Lecture 3: Motion in 1-D, part II

2. PHY 231 2 Previously… VECTORS Displacement Average Velocity Instantaneous velocity Average acceleration Instantaneous acceleration SCALARS Distance Average speed Instantaneous speed MOTION DIAGRAMS

3. PHY 231 3 example time x Draw v vs. t and a vs. t v 0 a

4. PHY 231 4

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6. 6 Constant acceleration Velocity at t=t equals… Velocity at t=0… Plus the gain in velocity per second Multiplied by the time span (every second, the velocity increases With a m/s)

7. PHY 231 7 Constant acceleration II Start position plus average speed multiplied by time Substitute

8. PHY 231 8 Important things! t x(m) t v m/s t a m/s 2 t x(m) t v m/s t a m/s 2 t x(m) t v m/s t a m/s 2 Constant motion Constant velocity Constant acceleration x(t)=x 0 +v 0 t+½at 2 x(t)=x 0 +v 0 t x(t)=x 0 v(t)=v 0 +at v(t)=v 0 v(t)=0 a(t)=a 0 a(t)=0

9. PHY 231 9 Free fall A 5 kg 1 kg 100 m B a is the the acceleration felt due to gravitation (commonly called g=9.8 m/s 2 ) Why no mass dependence???

10. PHY 231 10 T (s) v (m/s) 0 0 t=1,v=2 2 1)What is the distance covered in 1 second? 2)What is the area indicated by ? T (s) v (m/s) 0 0 t=1,v=2 2 Q 1. 2. a) 1. 1. b) 1. 2. c) 2. 1. d) 2. 2.

11. PHY 231 11 Kinematics in sports

12. PHY 231 12 100 m dash: what is the best strategy? After long training Ben Lewis can accelerate with a=3.00 m/s 2 over a distance of 20.0 m. Over the remaining 80.0 m, he can maintain this top-speed. A) After how many seconds reaches Ben top-speed? B) What is his speed at that time? C) In how much time does he cross the finish line?

13. PHY 231 13 After a lot of training... Ben manages to accelerate the first 3.65 s with a=4.00 m/s 2. After reaching his top-speed, he cannot maintain it however, and slowly de-accelerates (a=-0.4 m/s 2 ). Did his total time improve over 100 m? A) What distance does Ben cover while accelerating? B) What is his speed at that time? C) How long does is take to cover to remaining distance and what is his total time?

14. PHY 231 14 ????