Zero 3.7 m/s 2, downward 7.4 m/s 2, upward 7.4 m/s 2, downward 3.7 m/s 2, upward

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Mercy Peters
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1 PracticeExam2 1. A plastic ball in a liquid is acted upon by its weight and by a buoyant force. The weight of the ball is 2.5 N. The buoyant force has a magnitude of 4.4 N and acts vertically upward. At a given instant, the ball is released from rest. The acceleration of the ball at that instant, including direction, is closest to: Zero 3.7 m/s 2, downward 7.4 m/s 2, upward 7.4 m/s 2, downward 3.7 m/s 2, upward 2. Two weights are connected by a massless wire and pulled upward with a constant speed of 1.50 m/s by a vertical pull P. The tension in the wire is T. For this situation: P = T + 25 N T>P P + T = 125 N P = T N T=P 3. A block is on a frictionless table, on earth. The block accelerates at 3.3 m/s 2 when a 10 N horizontal force is applied to it. The block and table are set up on the moon. The acceleration due to gravity at the surface of the moon is 1.62 m/s 2. A horizontal force, equal in magnitude to the weight of the block on earth, is applied to the block when it is on the moon. The acceleration imparted to the block is closest to: 4 m/s 2 2 m/s 2 6 m/s 2 8 m/s 2 10 m/s 2 4. An astronaut who weighs 725 N on earth goes to planet X, which has no atmosphere. She observes that when she drops a 2.35-kg stone from rest on planet X, it takes it 1.12 s to fall a distance of 3.82 m. The astronautʼs weight on planet X is closest to: 505 N 1180 N 1170 N 451 N 4420 N

2 5. A box with weight w = 770 N is on a rough surface, inclined at an angle of 37 degrees. The box is kept from sliding down (in equilibrium) by means of an external force F. The other forces acting on the box are the normal and friction forces, denoted by n and f. A force diagram, showing the four forces that act on the box, is shown in Fig The magnitude of f is 210 N. The magnitude of the external force F is closest to: 368 N 290 N 329 N 406 N 252 N 6. A box with weight 32 N is on a rough horizontal surface. An external force F is applied horizontally to the box. A normal force and a friction force are also present, denoted by n and f. A force diagram, showing the four forces that act on the box, is shown in the figure. When force F equals 8.6 N, the box is in motion at constant velocity. The box decelerates when force F is removed. The magnitude of the acceleration of the box is closest to: 0.67 m/s m/s m/s m/s 2 zero 7. A 20.0-N box rests on a 50.0-N box on a perfectly smooth horizontal floor. When a horizontal 15.0-N pull to the right is exerted on the lower box (see in the figure), both boxes move together. Find the magnitude and direction of the net external force on the upper box. Magnitude:?? N Direction: to the right to the left s on a 50.0-N box on a perfectly smooth horizontal floor. When a hor

3 8. A ball of mass 5.0 kg is suspended by two wires from a horizontal arm, which is attached to a vertical shaft, as shown in the figure. The shaft is in uniform rotation about its axis such that the linear speed of the ball equals 2.6 m/s. The tension in wire A is closest to: 21 N 8.5 N 4.3 N 17 N 13 N B 0.8 m 0.6 m 1.0 m A 9. In the figure, two wooden blocks of 0.30 kg mass each are connected by a string that passes over a pulley. One block slides on a horizontal table, while the other hangs suspended by the string, as shown in the sketch. At t = 0, the suspended block is 0.80 m over the floor, and the blocks are released from rest. After 2.5 s, the suspended block reaches the floor. What is the coefficient of kinetic friction between the table and the sliding block? Figure Two boxes are next to each other on a horizontal frictionless floor. A person exerts a horizontal N push on the lighter box, as shown in Fig As a result, the push that the lighter box exerts on the larger box is closest to: 75.0 N 50.0 N 80.0 N 20.0 N 25.0 N 11. A 4.00-kg box sits atop a 10.0-kg box on a horizontal table. The coefficient of kinetic friction between the two boxes and between the lower box and the table is 0.600, while the coefficient of static friction between these same surfaces is A horizontal pull to the right is exerted on the lower box, as shown in the

4 figure, and the boxes move together. The friction force on the upper box is closest to: 19.3 N to the left 31.4 N to the right 19.3 N to the right 23.5 N to the right 31.4 N to the left 12. A 1520-N crate is to be held in place on a ramp that rises at 30.0 above the horizontal (see in the figure). The massless rope attached to the crate makes a 22.0 angle above the surface of the ramp. The coefficients of friction between the crate and the surface of the ramp are µk= and" µs= The pulley has no appreciable mass or friction. What is the maximum weight w needed to hold this crate stationary on the ramp? Weight w:?? N A 1520-N crate is to be held in place on a ramp that rises at 30.0 above the horiz 13. In the figure, a constant external force P = 160 N is applied to a 20-kg box, which is on a rough horizontal surface. The force pushes the box a distance of 8.0 m, in a time interval of 4.0 s, and the speed changes from" v1 = 0.5 m/s to v2 = 2.6 m/s. The work done by friction is closest to: J J J J J 14. In the figure, a 700-kg crate is on a rough surface inclined at 30. A constant external force P = 5600 N is applied horizontally to the crate. The force pushes the crate a distance of 3.0 m up the incline, in a time interval of 7.3 s, and the velocity changes from v1 = 1.4 m/s to v2 = 2.5 m/s. The work done by the weight is closest to:

5 +10,200 J J J -10,200 J Zero 15. A 13.5 kg box slides over a rough patch 1.75 m long on a horizontal floor. Just before entering the rough patch, the speed of the box was 2.25 m/s, and just after leaving it, the speed of the box was 1.20 m/s. The average power consumed by friction on the rough patch is closest to: W 9.58 W 33.7 W 24.1 W It is impossible to know since we are not given the coefficient of kinetic friction. 16. A 60-kg person drops from rest a distance of 1.20 m to a platform of negligible mass supported by a stiff spring. The platform drops 6 cm before the person comes to rest. What is the spring constant of the spring? 5.45 x 10 4 N/m 3.92 x 10 5 N/m 8.83 x 10 4 N/m 2.56 x 10 5 N/m 4.12 x 10 5 N/m 17. A constant horizontal pull acts on a sled on a horizontal frictionless ice pond. The sled starts from rest. When the pull acts over a distance x, the sled acquires a speed v and a kinetic energy k. If the same pull instead acts over twice this distance: The sled's speed will be 2v and its kinetic energy will be 2k. The sled's speed will be 2v and its kinetic energy will be k 2. The sled's speed will be v 2" and its kinetic energy will be k 2. The sled's speed will be 4v and its kinetic energy will be 2k. The sled's speed will be v 2 and its kinetic energy will be 2k. Figure In the figure, a 0.80-m light rod is loosely pinned to a vertical shaft at A. A 2.0-kg disk is attached to the rod at B. A spring is attached to the rod at B and to a sleeve on the shaft at C. The sleeve is frictionless, allowing it to move freely up or down, so that the spring is always horizontal when stretched. The unstretched length of the spring is m and the force constant is 180 N/m. The shaft is in rotation and the spring has a stretched length of m. The radial acceleration of

6 the disk is closest to: 11.5 m/s m/s m/s m/s m/s A certain car traveling 32.0 mph skids to a stop in 35 meters from the point where the brakes were applied. In approximately what distance would the car stop had it been going 89.6 mph? 98 m 35 m 164 m 274 m 59 m 20. In the figure, a block of mass M hangs in equilibrium. The rope that is fastened to the wall is horizontal and has a tension of 55 N. The rope that is fastened to the ceiling has a tension of 63 N, and makes an angle θ with the ceiling. The angle θ is: A series of weights connected by very light cords are given an upward acceleration of 4.00 m/s 2 by a pull P, as shown in the figure. A, B, and C are the tensions in the connecting cords. The pull P is closest to: 200 N 50 N 290 N 690 N 490 N

7 22. A system comprising blocks, a light frictionless pulley, and connecting ropes is shown. The 9-kg block is on a smooth horizontal table ("µ = 0). The surfaces of the 12-kg block are rough, with µ= In the figure, the mass M is set so that it descends at constant velocity when released. The mass M is closest to: 3.3 kg 2.7 kg 3.6 kg 2.4 kg 3.0 kg g blocks, a light frictionless pulley, and connecting ropes is shown. The 9 SOLUTIONS m/s 2, upward 2. P = T + 25 N m/s N N m/s N, to the right N N N to the right N J ,200 J W x 10 5 N/m 17. The sledʼs speed will be v 2 and the kinetic energy will be 2k m/s m N kg

C B A T 3 T 2 T 1. 1. What is the magnitude of the force T 1? A) 37.5 N B) 75.0 N C) 113 N D) 157 N E) 192 N

C B A T 3 T 2 T 1. 1. What is the magnitude of the force T 1? A) 37.5 N B) 75.0 N C) 113 N D) 157 N E) 192 N Three boxes are connected by massless strings and are resting on a frictionless table. Each box has a mass of 15 kg, and the tension T 1 in the right string is accelerating the boxes to the right at a