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Unformatted text preview: homework 15 PAPAGEORGE, MATT Due: Feb 23 2008, 4:00 am 1 Question 1, chap 7, sect 3. part 1 of 3 10 points A block of mass m is pushed a distance D up an inclined plane by a horizontal force F . The plane is inclined at an angle with respect to the horizontal. The block starts from rest and the coefficient of kinetic friction is k . m D k F If N is the normal force, what is the work done by friction? 1. W = + k N D 2. W = + k ( N  mg cos ) D 3. W = 0 4. W = k ( N + mg cos ) D 5. W = k N D correct 6. W = + k ( N + mg cos ) D 7. W = k ( N  mg cos ) D Explanation: The force of friction has a magnitude F friction = k N . Since it is in the direc tion opposite to the motion, we get W friction = F friction D = k N D. Question 2, chap 7, sect 3. part 2 of 3 10 points What is the work done by the normal force N ? 1. W = ( N + mg cos + F sin ) D 2. W =N D 3. W = 0 correct 4. W = N D 5. W = N D sin 6. W = ( N  mg cos  F sin ) D 7. W = ( mg cos + F sin N ) D 8. W = N D cos Explanation: The normal force makes an angle of 90 with the displacement, so the work done by it is zero. Question 3, chap 7, sect 3. part 3 of 3 10 points What is the final speed of the block? 1. v = radicalbigg 2 m ( F sin + k N ) D 2. v = radicalbigg 2 m ( F cos  mg sin ) D 3. v = radicalbigg 2 m ( F cos  mg sin  k N ) D correct 4. v = radicalbigg 2 m ( F cos  mg sin + k N ) D 5. v = radicalbigg 2 m ( F sin  k N ) D 6. v = radicalbigg 2 m ( F cos  k N ) D 7. v = radicalbigg 2 m ( F cos + mg sin  k N ) D 8. v = radicalbigg 2 m ( F cos + mg sin ) D Explanation: The work done by gravity is W grav = mg D cos(90 + ) = mg D sin . homework 15 PAPAGEORGE, MATT Due: Feb 23 2008, 4:00 am 2 The work done by the force F is W F = F D cos . From the workenergy theorem we know that W net = K , W F + W grav + W friction = 1 2 mv 2 f ....
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This note was uploaded on 03/02/2009 for the course PHY 58235 taught by Professor Kleinman during the Spring '09 term at University of Texas at Austin.
 Spring '09
 KLEINMAN
 Physics, Force, Mass, Work

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