Explain to each other your movie project and the variable you are calculating. Discuss how will you know if it could occur in real life.

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Dorothy McCormick
5 years ago
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1 Movie Review Pat One due today! (tun in now please) Pick a peson that you did NOT do the movie poposal with. Explain to each othe you movie poject and the vaiable you ae calculating. Discuss how will you know if it could occu in eal life.

2 Last Time: Linea Momentum & Impulse p = mv Units: kg m/s Linea momentum of an object is mass times velocity Linea momentum is a vecto. Diection of linea momentum is the same as the velocity of the object F net = p t I = p = F t 1. A foce must act on an object fo impulse to occu 2. In a collision, an impulse occus in the diection of the foce acting on the object

3 Main Ideas in Class Today Afte today s class, you should be able to: Undestand what a system is and detemine whethe it is isolated Apply Consevation of Linea Momentum to detemine a final velocity in one o two dimensions Exta Pactice: 6.21, 6.23, 6.27, 6.65

4 What is a System? A system is a set of objects inteacting with each othe (set of pool balls, ball/bat, students in this oom) An isolated system has no unbalanced extenal foces, meaning no unbalanced foces outside the system (e.g., nomal/gavity) In an isolated system F net,system =0 because of Newton s Thid Law: F 12 = F 21 F = F + F net, system F net = 0, system

5 Isolated System? Ignoe ai esistance. A.Yes. B.No. Cas cashing on ice Two boats cash (ignoe fiction, small) Q66-68 Jumping guy hits socce ball in ai

6 Isolated System? Did ca s/zombie s velocity matte? A.Yes. Ca and Zombie moving with constant velocity (befoe and afte hitting each othe) B.No. Q69-70

Even if a system isn t isolated, often we

much time to act) Would wok fine Would not

7 Even if a system isn t isolated, often we can appoximate it as isolated by only consideing just befoe and afte the instant of the collision (othe foces don t have much time to act) Would wok fine Would not wok hee (extenal foce has a lage impact on the esult)

8 Main Ideas in Class Today Afte today s class, you should be able to: Undestand what a system is and detemine whethe it is isolated Apply Consevation of Linea Momentum to detemine a final velocity in one o two dimensions Exta Pactice: 6.21, 6.23, 6.27, 6.65

9 Thee is Consevation of Linea Momentum in Isolated Systems. Initial (i) While not isolated in the y diection, can use momentum fomula in x Final (f ) diection. This is a vecto fomula. What does that mean? F = 0 net, system p F net system N s 2nd Law: psystem, system = = 0 t = p p f, system i, system = p = p f, system i, system Ex: collision of two billiad balls on a fictionless suface v + m v = m v + m v m 1 1i 2 2i 1 1 f 2 2 f 0

10 Recoil A ifle with a weight (W=mg) of 20 N fies a 4.0 g bullet with a speed of 280 m/s. (a) Find the ecoil speed of the ifle. (b) If a 725 N man holds the ifle fimly against his shoulde, find the ecoil speed of the man and ifle. What is the system?

Consevation of momentum (golf) The head of a 0.2 kg golf club is taveling at 55 m/s just befoe it stikes a 0.046 kg golf ball at est on a tee.

11 Consevation of momentum (golf) The head of a 0.2 kg golf club is taveling at 55 m/s just befoe it stikes a kg golf ball at est on a tee. Afte the collision, the club head tavels (in the same diection) at 40 m/s. Find the speed of the golf ball just afte impact. Teat the system as isolated duing the instant of collision.

12 m 1 m 2 Colliding objects initial m 2 =2m 1 final Let m 2 =2m 1, so m 2 is twice as massive. Let s say you hit ball 1 with v 1i =10m/s into stationay ball 2, v 2i = 0 m/s. Let s say that afte the collision, ball 1 is stationay. (not always the case) What is the final velocity of ball 2? A) 5 m/s B) 10 m/s C) 20 m/s D) -5 m/s E) -20 m/s Q71

13 An open cat is olling to the left at a constant speed on a hoizontal suface. A package slides down a chute and lands in the cat. Which quantities have the same value just befoe and just afte the package lands in the cat? A. The hoizontal component of total momentum B. The vetical component of total momentum C. Both of the above D. None of the above Q72

14 A 500-kg feight package is dopped vetically onto a 1000-kg ail cat moving at 6 m/s. The package is moving at 3 m/s just befoe landing on the cat. Afte the dop, the speed of the cat and package is closest to: v i = 6 m/s A. 9 m/s B. 7 m/s C. 6 m/s D. 4 m/s E. 3 m/s Q73

15 How much will unning ove a zombie slow you down?

An astonaut in he space suit has a total mass of m 1 = 87 kg, including he oxygen tank. He tethe line loses its attachment to he spacecaft and she is too fa to gab on!

16 An astonaut in he space suit has a total mass of m 1 = 87 kg, including he oxygen tank. He tethe line loses its attachment to he spacecaft and she is too fa to gab on! Initially at est with espect to he spacecaft, she thows he oxygen tank of mass m 2 = 12.0-kg away fom he spacecaft with a speed v = 8.00 m/s to popel heself back towad the spacecaft. Detemine the maximum distance she can be fom the caft and still etun within 2.00 min (the amount of time the ai in he helmet emains beathable).

17 Foces of Motion Cas move due to the foce of fiction between the ties and oad. Planes take advantage of ai esistance. Boats use the esistance of the wate. But what about ockets in space? Thee is no ai in space to povide a esistance

18 The New Yok Times Response To Rockets in Space ("New Yok Times," 13 Januay, 1920, p. 12, col. 5) That Pofesso Goddad does not know the elation of action to eaction, and the need to have something bette than a vacuum against which to eact--to say that would be absud. Of couse he only seems to lack the knowledge ladled out daily in high schools. What do you think about this citique? 2 Lessons: Even billiant scientists make mistakes. And fequently, even expets don t agee.

19 Diet Coke and Mentos What does this have to do with ockets?

20 Rocket Populsion While it s tue that thee is no fiction to popel ockets fowad in space, thee is consevation of momentum. m p = p i, system f, system + = + i v m v m v m v i Instead of thowing the tank, imagine just letting the gas in the tank spay out (safe, but slowe) Note: Changing mass

21 Rocket video

22 Let s conside this situation again Could find ecoil of socce playe.

Example: A Runaway Raiload Ca A 14,000 kg aiload ca is olling at 4.00 m/s towad an intesection. As it passes a gain elevato, 2,000 kg of gain suddenly dops vetically into the ca.

23 Example: A Runaway Raiload Ca A 14,000 kg aiload ca is olling at 4.00 m/s towad an intesection. As it passes a gain elevato, 2,000 kg of gain suddenly dops vetically into the ca. Ignoe fiction and ai dag. How long does it take fo the ca to tavel the 500 m distance fom the gain elevato to the intesection? P Fi ext = Fg gain + Fg ca + Fn = t Conseved in x diection ( m + m ) v = m v + m (0) c g f x c ix g sys m v c f x = v ix m m c + g P = sys fx d( mc + mg ) (500 m)(14000 kg kg) d = v fx t t = = = 143 s m v (14000 kg)(4.00 m/s) c ix P sys ix

Cadiology (Challenging setup) In eseach of cadiology and execise physiology, it is often impotant to know the mass of blood pumped by a peson's heat in one stoke.

24 Cadiology (Challenging setup) In eseach of cadiology and execise physiology, it is often impotant to know the mass of blood pumped by a peson's heat in one stoke. This infomation can be obtained by means of a ballistocadiogaph. The instument woks as follows: The subject lies on a hoizontal pallet floating on a film of ai. Fiction on the pallet is negligible. Initially, the momentum of the system is zeo. When the heat beats, it expels a mass m of blood into the aota with speed v, and the body and platfom move in the opposite diection with speed V. The speed of the blood can be detemined independently. Assume that the blood's speed is 50.0 cm/s in one typical tial. The mass of the subject plus the pallet is 54.0 kg. The pallet moves m in s afte one heatbeat. Calculate the mass of blood that leaves the heat. Assume that the mass of blood is negligible compaed with the total mass of the peson.

25 Clicke Answes 1=D, 2=E, 3=D, 4=B, 5=C, 6=A, 7=C, 8=E, 9=A, 10=C, 11=B, 12=C, 13=E, 14=A, 15=B, 16=C, 17=B, 18=D, 19=A, 20=C, 21=B, 22=B (had), 23=A Ch.4A: 25=A, 26=B, 27=E, 28=C, 29=C, 30=D, 31=C, 32=D, 33=C, 34=B, 35=D Ch.4B: 36=A, 37=C, 38=B, 39=E, 40=B, 41=B, 42=C, 43=A Ch.4C: 44=B, 45=A, 46=A, 47=C, 48=C, 49=A Ch.5A: 50=C, 51=E, 52=D, 53=E, 54=D Ch.5B: 55=A, 56=D, 57=A, 58=A, 59=B, 60=B, 61=C, 62=D Ch.6A: 63=B, 64=A, 65=B Ch.6B: 66=B, 67=A, 68=B, 69=A, 70=B, 71=A, 72=A, 73=D

Main Ideas in Class Today

Main Ideas in Class Today After today s class, you should be able to: Understand what a system is and determine whether it is isolated Apply Conservation of Linear Momentum to determine a final velocity