A 30 o 30 o M. Homework #4. Ph 231 Introductory Physics, Sp-03 Page 1 of 4

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1 Hoework #4. Ph 231 Introductory Physics, Sp-03 Page 1 o 4 4-1A. A particle o ass 2 kg is initially at rest at the origin x = 0. I the only orce acting on the particle is a constant 4 in the x-direction, what is the agnitude o particle's velocity v x at tie t = 2 seconds? (a) 1/s (b) 2 /s (c) 4 /s (d) 8 /s (e) one o these is close. 4-2A. How ar does the particle in proble 4-1A ove during the 2 seconds? (a) 2 (b) 16 (c) 6 (d) 8 (e) 4 4-3A. eglecting air resistance, the orce(s) on a ootball at the top o its path ater being kicked is (are) (a) the orce due to the horizontal otion o the ootball. (b) the orce o gravity (c) the orce exerted by the kicker plus the orce o gravity. (d) the orce exerted by the earth plus the orce o gravity. (e) the orce due to the horizontal otion o the ootball plus the orce o gravity. 4-4A. our orces act on an object, A = 50 east, B = 40 north, C = 90 west, D = 70 south. hat is the agnitude o the net orce on the object? (a) 260 (b) 50 (c) 70 (d) 10 (e) one o these is close. 4-5A. hich one o these is the reaction orce to the gravitational orce on a block due to the Earth? The block is at rest on the ground. (a) The contact orce exerted on the block by the ground. (b) The weight o the block. (c) The contact orce exerted on the ground by the block. (d) The gravitational orce on the Earth due to the block. (e) one o these is the correct reaction orce. 4-6A. A ass = 15 kg is supported by the weightless strings shown at the right, and the angles shown are 30 o. How large is the tension in string A? (a) 176 (b) 87 (c) 75 (d) 15 (e) 150 A 30 o 30 o 4-7A. A 75 kg woan, hanging ro a 5 kg parachute, is alling with a constant terinal speed o 12 /s. The size o the orce exerted by the air on the cobination o the woan and the parachute is about: (a) 6.7 (b) 80 (c) 800 (d) 960 (e) There is not enough inoration to tell. 4-8A. Two asses = 10 kg and = 15 kg are connected by a assless string over a assless, rictionless pulley as shown at the right. hat is the agnitude o the acceleration o ass? Take g = 10 /s 2. (a) 0.2 /s 2 (b) 2 /s 2 (c) 6 /s 2 (d) 10 /s 2 (e) 5 /s 2 4-9A. In Proble 4.8A, how large is the tension in the string while the asses ove? (a) 30 (b) 15 (c) 100 (d) 50 (e) A. A ass hangs by a string ro the top o an elevator. or which o the ollowing will the tension in the string be largest? (a) The elevator is oving upward with constant speed. (b) The elevator is oving upward but its speed is slowing. (c) The elevator is oving downward with constant speed. (d) The elevator is oving downward but its speed is slowing. (e) The elevator is alling reely. 4-11A. hich one o the ollowing stateents is wrong? (a) It is possible or an object to ove when no orce acts on it. (b) An object with only one orce acting on it ust be accelerating. (c) I an object has zero acceleration, there can be no orces acting on it. (d) An object that is accelerating ust have a net orce acting upon it. (e) An object oving with constant velocity ust have no net orce acting upon it. 4-12A. A orce o agnitude 25 pushes horizontally on a 20 kg box sliding on lat ground with kinetic riction coeicient µ k = 0.1. hat is the acceleration o the box? (a) 5 /s 2 (b) 1.25 /s 2 (c) 0.5 /s 2 (d) 0.25 /s 2 (e) The orce isn t enough to accelerate the box.

2 Hoework #4. Ph 231 Introductory Physics, Sp-03 Page 2 o 4 Use the ollowing or probles 4-13A and 4-14A. A person pulls an = 20 kg box with a orce = 100 directed 45 o above the horizontal as shown at the right. 4-13A. About how large is the noral orce o the box upon the ground? (a) 130 (b) 200 (c) 70 (d) 140 (e) o 4-14A. I the coeicient o kinetic riction between the box and the ground is µ k = 0.20, how large is the box s acceleration? (a) 2.3 /s 2 (b) 1.6 /s 2 (c) 3.4 /s 2 (d) 3.0 /s 2 (e) zero; the riction orce is too large. 4-15A. A child o ass = 5 kg sits in an open cart o ass =20 kg. A horse pulling the cart exerts a horizontal orce = 10 on the cart which accelerates the cart. eglect riction between the cart wheels and the ground. About how large is the horizontal orce that the cart exerts on the child? (a) 10 (b) 2.5 (c) 50 (d) 2 (e) There isn't enough inoration to tell. 4-16A. A block o weight = g is sliding down a plane that has riction. hich one o the ollowing pictures is a coplete and correct ree-body diagra or the block? a) b) c) d) e) Use the igure at the right or probles 4-17A and 4-18A A block o ass 50 kg is ree to slide up or down a plane that akes angle o 37 o with the horizontal. Take g = 10 /s A. I there is no riction, how large a orce is needed to hold the block ixed? (a) 300 (b) 500 (c) 400 (d) 100 (e) o 4-18A. I the coeicient o static riction is µ s = 0.20, what size orce will push the block up the plane at constant speed? (a) 220 (b) 420 (c) 580 (d)200 (e) 380

3 Hoework #4. Ph 231 Introductory Physics, Sp-03 Page 3 o 4 4-1B. A block o ass 3 kg, sliding on a horizontal rictionless surace, starts with velocity v x = 10 /s is subjected to a constant horizontal orce o size 9 or 4 seconds. hat is the particle s speed v at tie t = 4 sec? (a) 22 /s (b) 12 /s (c) 91 /s (d) 71 /s (e) one o these is close. 4-2B. How ar does the block o proble 4-1B ove in the 4 seconds? (a) 56 (b) 40 (c) 72 (d) 24 (e) B. eglecting air resistance, the orce(s) on a ootball while it is descending ater being kicked is (are) (a) the orce due to the horizontal otion o the ootball. (b) the orce exerted by the earth plus the orce o gravity (c) the orce exerted by the kicker plus the orce o gravity. (d) the orce o gravity. (e) the orce due to the horizontal otion o the ootball plus the orce o gravity. 4-4B. our orces act on an object, A = 50 east, B = 20 north, C = 100 west, D = 70 south. About what is the agnitude o the net orce on the object? (a) 60 (b) 50 (c) 70 (d) 150 (e) one o these is close. 4-5B. hich one o these is the reaction orce to the contact orce exerted on a block by the ground on which the block sits. (a) The gravitational orce exerted on the block due to the Earth. (b) The weight o the block. (c) The contact orce exerted on the ground by the block. (d) The gravitational orce exerted on the Earth due to the block. (e) one o these is the correct reaction orce. 4-6B. A ass = 1.0 kg is supported by the weightless strings shown at the right. I the angle shown is 45 o, about how large are the tensions in strings A and B (in that order)? Take g = 10 /s 2. (a) 10 t, 14 t (b) 10 t, 10 t (c) 14 t, 14 t (d) 14 t 10 t (e) one o these. 4-7B. A 5 kg parachute is alling with a constant terinal speed o 12 /s. I g = 10 /s 2, the agnitude o the orce being exerted by the air on the parachute is about: (a) 10 (b) 5 (c) 100 (d) 50 (e) There is not enough inoration to tell. 4-8B. Two asses = 4 kg and = 12 kg are connected together by a assless string over a assless and rictionless pulley as shown at the right. hat is the agnitude o the acceleration o the 12 kg ass? (a) 5 /s 2 (b) 10 /s 2 (c) 8 /s 2 (d) 0.5 /s 2 (e) 6.7 /s 2 B A 45 o 4-9B. In proble 4-8B, how large is the tension in the string while the asses ove? (a) 60 (b) 120 (c) 30 (d) 40 (e) one o these is close. 4-10B. A person weighs 70 on a scale on the bathroo loor. I the person carries that scale onto an elevator, and stands on it while the elevator oves, which one o the ollowing stateents is ROG? (a) The scale will read less than 70 when the elevator is oving downward with increasing speed. (b) The scale will read 70 when the elevator is at rest. (c) The scale will read ore than 70 when the elevator is oving upward, but with decreasing speed. (d) The scale will read 70 when the elevator is oving upward with constant speed. (e) The scale will read ore than 70 when the elevator is oving downward, but with decreasing speed. 4-11B. hich one o the ollowing stateents is wrong? (a) An object cannot ove unless a orce acts on it. (b) An object with only one orce acting on it ust be accelerating. (c) I an object has zero acceleration, there can be no net orce acting upon it. (d) An object that is accelerating ust have a net orce acting upon it. (e) An object oving with constant velocity ust have no net orce acting upon it. 4-12B. A orce o agnitude 50 pushes horizontally on a 20 kg box sliding on lat ground with kinetic riction coeicient µ k = 0.2. How large is the acceleration o the box? (a) 5 /s 2 (b) 1.25 /s 2 (c) 0.5 /s 2 (d) 25 /s 2 (e) The orce isn t enough to accelerate the box.

4 Hoework #4. Ph 231 Introductory Physics, Sp-03 Page 4 o 4 Use the ollowing or probles 4-13B and 4-14B. A an pushes a 15 kg box with a orce o 100 directed 45 o below the horizontal as shown at the right 4-13B. About how large is the noral orce o the box upon the ground? (a) 80 (b) 200 (c) 50 (d) 120 (e) o 4-14B. I the coeicient o kinetic riction between the box and the ground is µ k = 0.10, about how large is the box s acceleration? (a) 3.3 /s 2 (b) 6.2 /s 2 (c) 2.0 /s 2 (d) 3.7 /s 2 (e) zero; the riction orce is too large. 4-15B. A child o ass 6 kg rides in a cart o ass 24 kg. The horse pulling the cart exerts a horizontal orce = 15 on the cart, which accelerates the cart and child. eglect riction between the cart wheels and the ground. About what is the agnitude o the horizontal orce the child exerts on the cart? (a) 15 (b) 1.5 (c) 4 (d) 3 (e) There isn't enough inoration to tell. 4-16B. A block o weight = g is sliding up a plane that has riction. hich one o the ollowing pictures is a coplete and correct ree-body diagra or the block? (a) (b) (c) (d) (e) Use the igure at the right or probles 4-17B and 4-18B. A block o ass 50 kg is ree to slide up or down a plane that akes angle o 53 o with the horizontal. Take g = 10 /s B. I the coeicient o kinetic riction is µ k = 0.2, about how large will be the acceleration o the block down the plane? (a) 8 /s 2 (b) 7 /s 2 (c) 6 /s 2 (d) 5 /s 2 (e) one o these is close. 53 o 4-18B. I the coeicient o kinetic riction is µ k = 0.2, what size iniu additional orce is needed to ake the block slide down the plane with constant speed? (a) 460 (b) 340 (c) 300 (d) 600 (e) one o these is close.

5 4-1A) c 2A) e 3A) b 4A) b 5A) d 6A) e 7A) c 8A) b 9A) e 10A) d 11A) c 12A) d 13A) a 14A) a 15A) d 16A) d 17A) a 18A) e 4-1B) a 2B) e 3B) d 4B) c 5B) c 6B) d 7B) d 8B) a 9B) a 10B) c 11B) a 12B) c 13B) e 14B) a 15B) d 16B) a 17B) b 18B) b