Phy 231 Sp 02 Homework #6 Page 1 of 4

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1 Py 231 Sp 02 Homework #6 Page 1 of 4 6-1A. Te force sown in te force-time diagram at te rigt versus time acts on a 2 kg mass. Wat is te impulse of te force on te mass from 0 to 5 sec? (a) 9 N-s (b) 6 N-s (c) 5 N-s (d) 8 N-s (e) 10 N-s 6-2A. Te force in te force-time diagram of 6-1A acts for 5 sec on a 2 kg mass tat is initially at rest. Wat is te final speed of te mass? (a) 2 m/s (b) 3 m/s (c) 4 m/s (d) 5 m/s (e) 8 m/s Force (N) Time (sec) 6-3A. An object of mass m, moving to te rigt wit speed v, collides ead-on in a perfectly inelastic collision wit an object of twice te mass but alf te speed moving in te opposite direction. Wat is te speed of te combined mass after te collision? (a) zero (b) v/2 (c) v (d) 2v (e) None of tese is correct. 6-4A. Te two blocks sown at te rigt slide witout friction on flat ground. Wat is te speed v of te 2 kg block after te collision? Before Collision (a) 1 m/s (b) 2 m/s (c) 3 m/s (d) 4 m/s (e) You can't tell witout knowing if te collision is elastic. After Collision 1 kg 8 m/s 1 m/s 2 kg 2 m/s 1 kg 2 kg v 6-5A. A man of mass = 70 kg standing on a frictionless surface trows a ball of mass m = 7 kg forward wit velocity v = + 10 m/s. Wat velocity does te man acquire as a result? (a) - 1 m/s (b) + 1 m/s (c) - 10 m/s (d) + 10 m/s (e) None, because tere is no friction. 6-6A. A 0.10 kg object moving initially wit velocity v = 0.20 m/s eastward collides ead-on and elastically wit a second 0.10 kg object initially at rest. Wat is te velocity of te first 0.10 kg object after te collision? (a) 0.16 m/s eastward. (b) 0.16 m/s westward. (c) 0.04 m/s eastward. (d) 0.04 m/s westward. (e) zero. 6-7A. A skater is standing still on frictionless ice. Her friend trows a Frisbee straigt to er. In wic of te following cases is te final magnitude of momentum transferred to te skater largest? (a) Se catces te Frisbee and olds onto it. (b) Se catces te Frisbee momentarily, and ten drops it straigt down. (c) Se catces te Frisbee momentarily, and ten trows it back to er friend. (d) Se catces te Frisbee momentarily, and ten trows it in a direction opposite to tat of er friend. (e) All four of te above processes involve te same final momentum transfer to te girl. 6-8A. A block of mass m 1 = 3 kg slides down, from rest, from a eigt = 3.2 m above te ground on a frictionless ill tat makes an angle of 37 o wit te orizontal as sown at te rigt. Te block ten slides on frictionless flat ground until it its and sticks to a mass m 2 = 1 kg tat was initially at rest. Wat is te speed of te composite mass? (a) 2 m/s (b) 3 m/s (c) 4 m/s (d) 5 m/s (e) 6 m/s m 1 37 o m 2 6-9A. A projectile in fligt explodes into several fragments. Te total momentum of te fragments immediately after te explosion: (a) is te same as immediately before te explosion. (b) as been canged into kinetic energy of te fragments. (c) is less tan immediately before te explosion. (d) is more tan immediately before te explosion. (e) none of tese is correct. 6-10A. A 10.0 g bullet is fired into a 200-g block of wood tat is initially at rest on a orizontal surface tat as coefficient of kinetic friction µ k = If, after impact, te block slides 8 m before coming to rest, wat was te speed of te bullet before te collision? (a) 8 m/s (b) 168 m/s (c) 119 m/s (d) 286 m/s (e) 336 m/s

2 Py 231 Sp 02 Homework #6 Page 2 of A. If two different masses ave te same kinetic energy, ten teir momenta are: (a) proportional to te square of teir masses. (b) inversely proportional to teir masses. (c) proportional to teir masses. (d) inversely proportional to te square root of teir masses. (e) proportional to te square root of teir masses. 6-12A. Wic one of te following statements is WRONG? (a) A person sitting in a car tat runs into a brick wall sould experience te same impulse in stopping, weter or not te car as an airbag. (b) Wen two moving masses collide and stick togeter, te total kinetic energy of te system always decreases due to te collision. (c) If a veicle of mass m going nort at speed v collides inelastically wit an identical veicle going east at speed v, and te two veicles stick togeter, ten te combined mass sould move off to te nort-east (i.e., at an angle of 45 o wit respect to bot nort and east). Neglect friction wit te ground. (d) If a moving mass A collides elastically wit a mass B tat is initially at rest, te momentum transferred to B becomes smaller as B becomes eavier. (e) If a car and a large truck are involved in a ead-on, perfectly elastic collision, te magnitude of te cange in momentum of eac is te same. 6-13A. Wic one of te following statements is WRONG? (a) If a ligt and a eavy body ave equal kinetic energies, ten te ligt mass as te smaller momentum. (b) Total momentum will be conserved in an inelastic collision, so long as no external force acts on te colliding particles. (c) You soot a particle of mass m 1 at a particle of mass m 2 tat is initially at rest. To ave m 1 recoil (rebound) backward wit te largest possible speed, you want m 2 to be as ligt as possible. (d) If a ligt and a eavy body ave equal momenta, ten te eavier one will ave te smaller kinetic energy (e) Total momentum will be conserved in an elastic collision, so long as no external force acts on te colliding particles 6-14A. A massless spring of force constant k = 50 N/m is compressed a distance x = 0.2 m from its unstretced lengt and placed between two equal masses = 0.1 kg as sown at te rigt. Te system is initially at rest, eld togeter by a massless string. If te spring breaks, te speed of eac mass will be about: (a) 4.5 m/s (b) 10 m/s (c) 5 m/s (d) 3.2 m/s (e) 6.3 m/s Initial state Final state 6-15A. A mass m 1 = 2 kg slides along a orizontal surface tat as a coefficient of kinetic friction µ = 0.1 until it collides wit a second mass m 2 = 2 kg tat is initially at rest. If te two masses stick togeter and stop in a distance x = 1m, wat was te speed of m 1 just before te collision? (a) 1 m/s (b) 2.8 m/s (c) 4.9 m/s (d) 1.4 m/s (e) 2 m/s.

3 Py 231 Sp 02 Homework #6 Page 3 of 4 6-1B. Te force sown in te force-time diagram at te rigt acts on a 2 kg mass. Wat is te impulse of te force on te mass? (a) 8 N-s (b) 4 N-s (c) 32 N-s (d) 12 N-s (e) 16 N-s 6-2B. For te force-time diagram of Fig. 6-1B, wat is te final speed of te 2 kg mass if its initial speed is 2.0 m/s? (a) 6 m/s (b) 8 m/s (c) 12 m/s (d) 3 m/s (e) None of tese is close. Force (N) Time (sec) 6-3B. A mass of 3 kg, initially sliding to te rigt wit speed v = 8 m/s on a orizontal frictionless surface, collides inelastically wit a mass of 9 kg tat is initially at rest, so tat te two masses stick togeter. Wat is te speed of te composite mass? (a) 2.7 m/s (b) 32 m/s (c) 4 m/s (d) 2 m/s (e) 8 m/s 6-4B. Tree carts of masses 4.0 kg, 10 kg, and 3.0 kg move on a frictionless orizontal track wit speeds of 5.0 m/s, 3.0 m/s, and 4.0 m/s as sown at te rigt. Te carts stick togeter after colliding. Find te final velocity of te resulting composite cart. (Q: Does it matter weter te carts collide and stick at te same time?) (a) m/s, no (b) +2.2 m/s, no (c) 2.2 m/s, yes (d) 3.6 m/s, yes (e) m/s, yes 5.0 m/s 4 gm 3.0 m/s m/s 10 gm 3 gm 6-5B. Two masses, m 1 = 4.0 kg and m 2 = 2.0 kg are initially at rest at te same eigt = 5.0 m above te ground on frictionless ills wit te angles sown at te rigt. If te two masses slide down teir ills, collide on te flat ground, and stick togeter, to wat eigt, and up wic ill, does te combined mass move? (a) 0.39 m, left ill (b) 0.39 m, rigt ill (c) 0.56 m, rigt ill (d) 0.56m, left ill (e) None of tese is correct. m 1 m 2 45 o 37 o 6-6B. A 1 kg object moving initially wit velocity v = 2 m/s eastward collides ead-on and elastically wit a 1 kg object initially at rest. Wat is te velocity of te second 1 kg object after te collision? (a) zero (b) 1 m/s westward. (c) 1 m/s eastward. (d) 2 m/s westward. (e) 2 m/s eastward. 6-7B. A skater is standing still on frictionless ice trows a Frisbee straigt to a friend standing on solid ground. In wic of te following cases is te final magnitude of momentum transferred to te skater largest? (a) Te friend catces te Frisbee and olds onto it. (b) Te friend catces te Frisbee momentarily, and ten drops it straigt down. (c) Te friend catces te Frisbee momentarily, and ten trows it back to te skater wo catces it. (d) Te friend catces te Frisbee momentarily, and ten trows it in a direction opposite to tat of te skater. (e) All four of te above processes involve te same final momentum transfer to te skater. 6-8B. A mass m 1 = 3 kg, initially sliding to te rigt wit speed v o = 8 m/s on a orizontal frictionless surface, collides inelastically wit a mass m 2 = 1 kg tat is initially at rest, so tat te two masses stick togeter and slide up a frictionless incline tat makes an angle of 30 o wit te orizontal. Wat is te maximum eigt to wic te masses rise? (a) 2.7 m (b) 0.2 m (c) 4 m (d) 1.8 m (e) 16 m v m o 1 m 2 30 o 6-9B. A projectile in fligt explodes into several fragments. Te total kinetic energy of te fragments immediately after te explosion: (a) is te same as immediately before te explosion. (b) as been canged into momentum of te fragments. (c) is more tan immediately before te explosion. (d) is less tan immediately before te explosion. (e) none of tese is correct.

4 Py 231 Sp 02 Homework #6 Page 4 of B. A 10.0 g bullet is fired into a 100-g block of wood tat is initially at rest on a orizontal surface tat as coefficient of kinetic friction µ k = If, after impact, te block slides 9 m before coming to rest, wat was te speed of te bullet before te collision? (a) 33 m/s (b) 66 m/s (c) 33 m/s (d) 86 m/s (e) 128 m/s 6-11B. If two different masses ave te same momenta, ten teir kinetic energies are: (a) proportional to teir masses. (b) proportional to te square of teir masses. (c) proportional to te square root of teir masses. (d) inversely proportional to te square root of teir masses. (e) inversely proportional to teir masses. 6-12B. Wic one of te following statements is WRONG? (a) A person sitting in a car tat runs into a brick wall sould experience a smaller impulse in stopping if te car as an airbag. (b) Wen two moving masses collide and stick togeter, te total kinetic energy of te system always decreases due to te collision. (c) If a veicle of mass m going nort at speed v collides inelastically wit an identical veicle going east at speed v, and te two veicles stick togeter, ten te combined mass sould move off to te nort-east (i.e., at an angle of 45 o wit respect to bot nort and east). Neglect friction wit te ground. (d) If a moving mass A collides elastically wit a mass B tat is initially at rest, te momentum transferred to B becomes larger as B becomes eavier. (e) If a car and a large truck are involved in a ead-on, perfectly elastic collision, te magnitude of te impulse eac exerts on te oter is te same. 6-13B. Wic one of te following statements is WRONG? (a) If a ligt and a eavy body ave equal kinetic energies, ten te ligt mass as te larger momentum. (b) Total momentum will be conserved in an inelastic collision, so long as no external force acts on te colliding particles. (c) If a ligt and a eavy body ave equal momenta, ten te eavier one will ave te smaller kinetic energy (d) Total momentum will be conserved in an elastic collision, so long as no external force acts on te colliding particles (e) You soot a particle of mass m 1 at a particle of mass m 2 tat is initially at rest. To ave m 1 recoil (rebound) backward wit te largest possible speed, you want m 2 to be as eavy as possible. 6-14B. A massless spring of force constant k = 50 N/m is compressed a distance x = 0.1 m from its unstretced lengt and placed between two equal masses = 0.2 kg as sown at te rigt. Te system is initially at rest, eld togeter by a massless string. If te spring breaks, te speed of eac mass will be about: (a) 0.8 m/s (b) 1.1 m/s (c) 0.7 m/s (d) 1.6 m/s (e) 2.2 m/s Initial state Final state 6-15B. A mass m 1 = 4 kg slides along a orizontal surface tat as a coefficient of kinetic friction µ = 0.1 until it collides wit a second mass m 2 = 2 kg tat is initially at rest. If te two masses stick togeter and stop in a distance x = 1m, wat was te speed of m 1 just before te collision? (a) 1 m/s (b) 2.8 m/s (c) 4.9 m/s (d) 2.1 m/s (e) 1.4 m/s

5 6-1A) d 2A) c 3A) a 4A) b 5A) a 6A) e 7A) c 8A) e 9A) a 10A) b 11A) e 12A) d 13A) c 14A) d 15A) b 6-1B) e 2B) a 3B) d 4B) b 5B) c 6B) e 7B) c 8B) d 9B) c 10B) b 11B) e 12B) a 13B) a 14B) b 15B) d