1. Tuesday- Physics Con A homework Newton’s laws

2. Homework Question #1 A record of travel along a straight path is as follows: –Start from rest with constant acceleration of 2.77 m/s 2 for 10 s –Constant velocity for next 2.05 min –Constant negative acceleration (-9.47 m/s 2 ) for 4.39 s Find the overall displacement fro the complete trip.

3. Answer #1 Part one: V i = 0, a = 2.77, (t = 10) identifier = v f D = v i t + ½ at 2 d = _____ V f = vi +atv f = ______ Part two: V f from the first part = v i and v f in the second part v = _________ a = 0 t = 2.05 min x 60 = 123 sec Several equation to chose from… d = ½(v i +v f )t

4. Answer #1 Part C: v f of the second part = v i of the third a = -9.47, t = 4.39 D = v i t + ½ at 2 d = __________ Overall displacement = the sum of D’s from each part

5. Problem #2 Killer whales routinely jump 7.5 meters above the water. What is their velocity as they leave the water in order to achieve this feat?

6. Answer #2 7.5 = d, a = -9.8 (freefall), v f = 0 Want v i Identifier is time V f 2 = v i 2 + 2ad

7. Problem #3 Two students are on a balcony 19.6 m above the street. One student (student A) throws the ball vertically downward at 14.7 m/s at the same instant the other student (student B) throws the ball vertically upward with same speed. The second ball just misses the balcony on the way down. a) What is the difference in their time in the air? b) What is the velocity of each ball the instant before it hits the ground? c) How far apart are the balls 0.8 s after they are thrown?

8. What do we know Student A for the whole flight D = -19.6 m, a = -9.8 m/s 2, v i = -14.7 m/s Want t (part a) and v f (part b) Since solving for t would mean using the quadratic formula… Solve for v f first Identifier is then t so use V f 2 = V i 2 + 2ad Final velocity = ________ (remember downward motion)

9. Student A Once final velocity is found, use to find t: Ant equation with t is possible, simplest is V f = V i +at t = __________

10. Student B Vi = +14.7, a = -9.8, d = -19.6 Repeat the procedure done to find v f, t for student A V f = ________, t = ________

11. Part C To answer part c: find the overall displacement between balls Find d of each D of student A You know a = -9.8, t = 0.8 s, vi = -14.7, want d Final velocity is the identifier Use d = v i t + ½ at 2 d =__________

12. Part C D of student B You know a = -9.8, t = 0.8 s, vi = +14.7, want d Final velocity is the identifier Use d = v i t + ½ at 2 d =__________ How far apart means add the magnitudes

13. Newton’s Laws of Motion 3 Laws Describes how motion is governed by forces

14. What is the First Law of motion?

15. First Law An object at rest, stays at rest An object in motion, stays at the same constant rate Unless acted upon by a net outside force

16. Inertia The measure of an object’s resistance to change in motion Related to how massive the object is Larger the mass, the more inertia

17. Auto Accidents

18. Questions Will you be able to continue to hold some one or some thing in an auto accident What will happen to Fluffy if the animal is in the back window-well of your sedan during a crash What happens to your body in a frontal crash versus a rear end collision?

19. What is the 2 nd law of motion?

20. 2 nd law If there is a change in motion (acceleration) Acceleration = net force / mass Rewrite as the equation: F net = ma

21. 3 rd Law For every action force there is an equal but opposite reaction force Fist-fight Any interactions between objects