HW6 - Chapter 7 Work and kinetic energy

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11/12/23, 8:13 PM HW6 - Chapter 7 Work and kinetic energy https://session.masteringphysics.com/myct/assignmentPrintView?assignmentID=10868042 1/7 HW6 - Chapter 7 Work and kinetic energy Due: 11:59pm on Monday, November 13, 2023 You will receive no credit for items you complete after the assignment is due. Grading Policy Problem 7.8 Part A What is the minimum work needed to push a 990- car 350 up along a 7.5 incline? Ignore friction. Express your answer using two significant figures. ANSWER: Correct Prelecture Concept Question 7.01 Part A A ball is thrown straight upward. How does the sign of the work done by gravity while the ball is traveling upward compare with the sign of the work done by gravity while the ball is traveling downward? ANSWER: Correct Problem 7.1 = 4.4×10 5 Work done by gravity is negative while the ball is traveling both upward and downward. Work done by gravity is positive while the ball is traveling both upward and downward. Work done by gravity is positive while the ball is traveling upward and negative while the ball is traveling downward. Work done by gravity is negative while the ball is traveling upward and positive while the ball is traveling downward.

11/12/23, 8:13 PM HW6 - Chapter 7 Work and kinetic energy https://session.masteringphysics.com/myct/assignmentPrintView?assignmentID=10868042 2/7 Part A How much work is done by the gravitational force when a 290- pile driver falls 2.80 ? Express your answer using two significant figures. ANSWER: Correct Pulling a Block on an Incline with Friction A block of weight sits on an inclined plane as shown in . A force of magnitude is applied to pull the block up the incline at constant speed. The coefficient of kinetic friction between the plane and the block is . Part A What is the total work done on the block by the force of friction as the block moves a distance up the incline? Express the work done by friction in terms of any or all of the variables , , , , , and . Hint 1. How to start Draw a free-body force diagram showing all real forces acting on the block. Hint 2. Find the magnitude of the friction force Write an expression for the magnitude of the friction force. Express your answer in terms of any or all of the variables , , , and . Hint 1. Find the magnitude of the normal force What is the magnitude of the normal force? = 8000

11/12/23, 8:13 PM HW6 - Chapter 7 Work and kinetic energy https://session.masteringphysics.com/myct/assignmentPrintView?assignmentID=10868042 3/7 Express your answer in terms of , , and . ANSWER: ANSWER: ANSWER: Correct Part B What is the total work done on the block by the applied force as the block moves a distance up the incline? Express your answer in terms of any or all of the variables , , , , , and . ANSWER: Correct Now the applied force is changed to , so that instead of pulling the block up the incline, the force pulls the block down the incline at a constant speed as shown in . Part C What is the total work done on the block by the force of friction as the block moves a distance down the incline? = = = =

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11/12/23, 8:13 PM HW6 - Chapter 7 Work and kinetic energy https://session.masteringphysics.com/myct/assignmentPrintView?assignmentID=10868042 4/7 Express your answer in terms of any or all of the variables , , , , , and . ANSWER: Correct Part D What is the total work done on the box by the appled force in this case? Express your answer in terms of any or all of the variables , , , , , and . ANSWER: Correct Problem 7.24 A constant force = 2.5 + 4.0 acts on an object as it moves along a straight-line path. If the object's displacement is =1.1 + 5.0 , calculate the work done by using these alternate ways of writing the dot product: Part A Calculate the work done by using these alternate ways of writing the dot product: . Express your answer using two significant figures. ANSWER: Correct Part B Calculate the work done by using these alternate ways of writing the dot product: . Express your answer using two significant figures. ANSWER: = = = 23 = 23

11/12/23, 8:13 PM HW6 - Chapter 7 Work and kinetic energy https://session.masteringphysics.com/myct/assignmentPrintView?assignmentID=10868042 5/7 Correct Problem 7.55 Part A If the kinetic energy of a particle is tripled, by what factor has its speed increased? ANSWER: Correct Part B If the speed of a particle is reduced to a third, by what factor does its kinetic energy change? ANSWER: Correct Problem 7.73 An elevator cable breaks when a 900 elevator is 22.0 above the top of a huge spring ( = 8.50×10 4 ) at the bottom of the shaft. Part A Calculate the work done by gravity on the elevator before it hits the spring. ANSWER: Correct = 1.73 = 0.111 = 1.94×10 5

11/12/23, 8:13 PM HW6 - Chapter 7 Work and kinetic energy https://session.masteringphysics.com/myct/assignmentPrintView?assignmentID=10868042 6/7 Part B Calculate the speed of the elevator just before striking the spring. ANSWER: Correct Part C Calculate the amount the spring compresses (note that here work is done by both the spring and gravity). ANSWER: Correct Problem 7.20 Part A Calculate the angle between the vectors: = 6.5 -3.9 -6.8 and = 8.5 +2.9 -6.9 . Express your answer using two significant figures. ANSWER: Correct Problem 7.39 The net force exerted on a particle acts in the positive direction. Its magnitude increases linearly from zero at , to 500 at = 3.0 . It remains constant at 500 from = 3.0 to = 6.0 , and then decreases linearly to zero at = 14.4 . Part A = 20.8 = 2.24 = 38

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11/12/23, 8:13 PM HW6 - Chapter 7 Work and kinetic energy https://session.masteringphysics.com/myct/assignmentPrintView?assignmentID=10868042 7/7 Determine the work done to move the particle from to = 14.4 graphically, by determining the area under the versus graph. Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Score Summary: Your score on this assignment is 100%. You received 9 out of a possible total of 9 points. = 4400

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