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Assignment Previewer Forces & Newton's Laws of Motion (496767) Previewer Tools Show All Hide All In View: Key Close this window Hidden: Assignment Score Mark Help/Hints Solution Show New

1 Assignment Previewer Forces & Newton's Laws of Motion (496767) Previewer Tools Show All Hide All In View: Key Close this window Hidden: Assignment Score Mark Help/Hints Solution Show New Randomization Open in Editor Details About this Assignment Due: Fri Sep :18 AM MDT 1. CJ6 4.P.004. [294566] Show Details Scientists are experimenting with a kind of gun that may eventually be used to fire payloads directly into orbit. In one test, this gun accelerates a 5.0 kg projectile from rest to a speed of m/s. The net force accelerating the projectile is N. How much time is required for the projectile to come up to speed? [0.0413] s 2. CJ6 4.P.011. [239481] Show Details Two forces, F 1 and F 2, act on the 5.00 kg block shown in the drawing. The magnitudes of the forces are F 1 = 59.5 N and F 2 = 39.5 N. What is the horizontal acceleration (magnitude and direction) of the block? [2.87] m/s 2 ---Select--- [ left ] 3. CJ6 4.P.013. [239483] Show Details Only two forces act on an object (mass = 4.30 kg), as in the drawing. (F = 51.0 N.) Find the magnitude and direction (relative to the x axis) of the acceleration of the object. [19.6] m/s 2 [25.4] (counterclockwise from the +x axis) 1 of 9 8/11/07 1:44 PM

2 4. CJ6 4.P.014. [294450] Show Details Airplane flight recorders must be able to survive catastrophic crashes. Therefore, they are typically encased in crash-resistant steel or titanium boxes that are subjected to rigorous testing. One of the tests is an impact shock test, in which the box must survive being thrown at high speeds against a barrier. A 41 kg box is thrown at a speed of 185 m/s and is brought to a halt in a collision that lasts for a time of 5.8 ms. What is the magnitude of the average net force that acts on the box during colision? [1.31e+06] N 5. CJ6 4.P.036. [294557] Show Details A woman stands on a scale in a moving elevator. Her mass is 57.0 kg, and the combined mass of the elevator and scale is an additional 815 kg. Starting from rest, the elevator accelerates upward. During the acceleration, the hoisting cable applies a force of 9740 N. What does the scale read during the acceleration? [637] N 6. CJ6 4.P.039. [498948] Show Details A 19.5 kg sled is being pulled across a horizontal surface at a constant velocity. The pulling force has a magnitude of 84.5 N and is directed at an angle of 30.0 above the horizontal. Determine the coefficient of kinetic friction. µ k = [0.492] 7. CJ6 4.P.044. [239490] Show Details The drawing shows a large cube (mass = 45 kg) being accelerated across a horizontal frictionless surface by a horizontal force P. A small cube (mass = 5.0 kg) is in contact with the front surface of the large cube and will slide downward unless P is sufficiently large. The coefficient of static friction between the cubes is What is the smallest magnitude that P can have in order to keep the small cube from 2 of 9 8/11/07 1:44 PM

sliding downward? [690] N 8. CJ6 4.P.046. [294443] Show Details Part a of the drawing shows a bucket of water suspended from the pulley of a well; the tension in the rope is 73.5 N.

3 sliding downward? [690] N 8. CJ6 4.P.046. [294443] Show Details Part a of the drawing shows a bucket of water suspended from the pulley of a well; the tension in the rope is 73.5 N. Part b shows the same bucket of water being pulled up from the well at a constant velocity. What is the tension in the rope in part b? [147] N 9. CJ6 4.P.050. [239493] Show Details The steel I-beam in the drawing has a weight of 7.50 kn and is being lifted at a constant velocity. What is the tension in each cable attached to its ends? [3990] N 3 of 9 8/11/07 1:44 PM

[294503] Show Details A 292 kg motorcycle is accelerating up along a ramp that is inclined 27.0 above the horizontal.

4 10. CJ6 4.P.067. [239498] Show Details In the drawing, the weight of the block on the table is 474 N and that of the hanging block is 200 N. Ignore all frictional effects, and assume the pulley to be massless. (a) Find the acceleration of the two blocks. [2.91] m/s 2 (b) Find the tension in the cord [141] N 11. CJ6 4.P.068. [294503] Show Details A 292 kg motorcycle is accelerating up along a ramp that is inclined 27.0 above the horizontal. The propulsion force pushing the motorcycle up the ramp is 3310 N, and air resistance produces a force of 250 N that opposes the motion. Find the magnitude of the motorcycle's acceleration. [6.03] m/s CJ6 4.P.079. [239502] Show Details A box is sliding up an incline that makes an angle of 14.0 with respect to the horizontal. The coefficient of kinetic friction between the box and the surface of the incline is The initial speed of the box at the bottom of the incline is 1.90 m/s. How far does the box travel along the incline before coming to rest? [0.442] m 4 of 9 8/11/07 1:44 PM

5 13. CJ6 4.P.084. [405078] Show Details As part a of the drawing shows, two blocks are connected by a rope that passes over a set of pulleys. One block has a weight of m 1 = 312 N, and the other has a weight of m 2 = 858 N. The rope and the pulleys are massless and there is no friction. (a) What is the acceleration of the lighter block? [4.57] m/s 2 (b) Suppose that the heavier block is removed, and a downward force of 858 N is provided by someone pulling on the rope, as part b of the drawing shows. Find the acceleration of the remaining block. [17.2] m/s 2 (c) Explain why the asnwers in (a) and (b) are different. Key: In the first case, the inertia of BOTH blocks affects the acceleration whereas, in the second case, only the lighter block's inertia remains. 14. CJ6 4.CQ.011. [310990] Show Details The force of air resistance acts to oppose the motion of an object moving through the air. A ball is thrown upward and eventually returns to the ground. (a) As the ball moves upward, is the net force that acts on the ball greater than, less than, or equal to its weight? (o) net force will be greater than the weight of the ball (_) net force will be lesser than the weight of the ball (_) net force will be equal to the weight of the ball 5 of 9 8/11/07 1:44 PM

6 Justify your answer. Key: The weight of the ball always acts downward. The force of air resistance will always act in the direction that is opposite to the direction of motion of the ball. The net force on the ball is the resultant of the weight and the force of air resistance. As the ball moves upward, the force of air resistance acts downward. Since air resistance and the weight of the ball act in the same direction in this case, the net force on the ball will be greater in magnitude than the weight of the ball. (b) Repeat part (a) for the downward motion of the ball. (_) net force will be greater than the weight of the ball (o) net force will be lesser than the weight of the ball (_) net force will be equal to the weight of the ball Justify your answer. Key: As the ball falls downward, the force of air resistance is upward. Since air resistance and the weight of the ball act in opposite directions, the net force that acts on the ball will be smaller in magnitude than the weight of the ball. 15. CJ6 4.CQ.015. [310901] Show Details A 10 kg suitcase is placed on a scale that is in an elevator. Is the elevator accelerating up or down when the scale reads the following? (a) 75 N (_) elevator is accelerating up (o) elevator is accelerating down (_) elevator has no acceleration Justify your answer. 6 of 9 8/11/07 1:44 PM

7 Key: When the apparent weight is F N = 75 N, the apparent weight is less than the true weight (mg = 98 N) so a must be negative. The elevator is accelerating downward. (b) 120 N (o) elevator is accelerating up (_) elevator is accelerating down (_) elevator has no acceleration Justify your answer. Key: When the apparent weight is F N = 120 N, the apparent weight is greater than the true weight (mg = 98 N) so a must be positive. The elevator is accelerating upward. 16. CJ6 4.CQ.018. [310920] Show Details A person has a choice of either pushing or pulling a sled at a constant velocity, as the drawing illustrates. Friction is present. If the angle is the same in both cases, does it require less force to push or to pull? (o) less force is required to pull the sled (_) equal force is required to either push or pull the sled (_) less force is required to push the sled Account for your answer. 7 of 9 8/11/07 1:44 PM

8 Key: Since the sled moves with constant velocity, the force of kinetic friction is present. The magnitude of this force is given by µ k F N, where µ k is the coefficient of kinetic friction and F N is the magnitude of the normal force that acts on the sled. Furthermore, the horizontal component of the applied force must be equal in magnitude to the force of kinetic friction, since there is no acceleration. When the person pulls the sled, the vertical component of the pulling force tends to decrease the magnitude of the normal force relative to that when the sled is not being pulled or pushed. On the other hand, when the person pushes the sled, the vertical component of the pushing force tends to increase the normal force relative to that when the sled is not being pulled or pushed. Therefore, when the sled is pulled, the magnitude of the force of kinetic friction, and therefore the magnitude of the applied force, is less than when the sled is pushed. 17. CJ6 4.CQ.026. [311067] Show Details A weight hangs from a ring at the middle of a rope, as the drawing illustrates. Can the person who is pulling on the right end of the rope ever make the rope perfectly horizontal? (_) yes (o) no (_) not enough information to decide Explain your answer in terms of the forces that act on the ring. Key: There are three forces that act on the ring as shown in the figure below: the weight of the block, which acts downward, and two forces of tension that act along the rope away from the ring. 8 of 9 8/11/07 1:44 PM

9 Since the ring is at rest, the net force on the ring is zero. The weight of the block is balanced by the vertical components of the tension in the rope. Clearly the rope can never be made horizontal, for then there would be no vertical components of the tension forces to balance the weight of the block. Submit for Testing 9 of 9 8/11/07 1:44 PM

Chapter 4. Forces and Newton s Laws of Motion. continued

Chapter 4. Forces and Newton s Laws of Motion. continued Chapter 4 Forces and Newton s Laws of Motion continued 4.9 Static and Kinetic Frictional Forces When an object is in contact with a surface forces can act on the objects. The component of this force acting