5 Newton’s Third Law of MotionAnswers and Solutions for Chapter 5 Reading Check Questions 1. The force is the wall pushing on your fingers. 2. Hecan’texertmuchforceonthetissuepaperbecausethepapercan’treactwiththesame magnitude of force. 3. Apairofforcesarerequiredforaninteraction. 4. Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object. 5. Action: bat against ball. Reaction: ball against bat. 6. Yes,andthatexternalnetforceacceleratestheorangesystem. 7. No,forthepairofforcesareinternaltotheapple-orangesystem. 8. Yes,anexternalnetforceisrequiredtoacceleratethesystem. 9. Yes,thenetforceisprovidedbycontactwithyourfoot.Iftwooppositeandequalforcesactonthe ball, the net force on it is zero and it will not accelerate. 10. Yes, you pull upward with the same amount of force on Earth. 11. The different accelerations are due to different masses. 12. The force that propels a rocket is the exhaust gases pushing on the rocket. 13. A helicopter gets its lifting force by pushing air downward, in which case the reaction is the air pushing the helicopter upward. 14. You cannot touch without being touched! And with the same amount of force. 15. Theprocessofdeterminingthecomponentsofavector. 16. Themagnitudeofthenormalforcedecreases. 17. The friction force has the same magnitude, with the sum of all forces being zero.
18. Moving upward, the vertical component of velocity decreases. The horizontal component remains constant, in accord with Newton’s first law. 19. Inertia; acceleration; action and reaction. 20. Newton’s third law deals with interactions. Think and Do 21.Your hand will be pushed upward, a reaction to the air it deflects downward. 22. Each will experience the same amount of force. Plug and Chug 23. 100 km/h – 75 km/h = 25 km/h north. 100 km/h + 75 km/h = 175 km/h north 24. R = √(1002 + 1002) = 141 km/h 25.R=√(42 +32)=5. 26. R = √(2002 + 802) = 215 km/h Think and Solve 27. a. a = ∆v/∆t =(25 m/s)/(0.05 s) = 500 m/s2. b. F = ma = (0.003 kg)(500 m/s2) = 1.5 N, which is about 1/3 pound. c. By Newton’s third law, the same amount, 1.5 N. 28.The wall pushes on you with 40 N. a = F/m = 40 N/80 kg = 0.5 m/s2. 29.a = F/m, where F = √[(3.0 N)2 + (4.0 N)2] = 5 N. So a = F/m = 5 N/2.0 kg = 2.5 m/s2. 30.(a)Fromthe3rdlaw Fon2mpuck = Fonmpuck Þ2m(a2m) = m(am) Þ2mDv2m =mDvm Since Dt Dt t h e f o r c e a c t s f o r e x a c t l y t h e s a m e D t f o r e a c h m a s s ÞD v 2 m = 21 D v m . S i n c e b o t h m a s s e s s t a r t o u t a t r e s t Þv 2 m = 12 v m . 11(m)m (b) v2m=2vm=2 0.4s =0.2s. Think and Rank 31. A = B = C 32. A, B, C; (b) B, C 33. (a) A = B = C; (b) C, B, A Think and Explain 34. Action;hammerhitsnail.Reaction;nailhitshammer.(b)Action;Earthpullsdownonabook. Reaction; book pulls up on Earth. (c) Action; helicopter blade pushes air downward. Reaction; air pushes helicopter blade upward. (In these examples, action and reaction may be reversed—which is called which is unimportant.)
35.In accord with Newton’s third law, Steve and Gretchen are touching each other. One may initiate the touch, but the physical interaction can’t occur without contact between both Steve and Gretchen. Indeed, you cannot touch without