This preview shows pages 1–3. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: homework 15 YOO, HEE 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 + mg cos ) D 2. W = k N D correct 3. W = k ( N  mg cos ) D 4. W = 0 5. W = + k ( N  mg cos ) D 6. W = k ( N + mg cos ) D 7. W = + k N 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 D 2. W = N D 3. W = 0 correct 4. W = ( mg cos + F sin N ) D 5. W = N D cos 6. W = ( N  mg cos  F sin ) D 7. W = N D sin 8. W = ( N + mg cos + F sin ) D 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  k N ) D 3. v = radicalbigg 2 m ( F sin  k N ) D 4. v = radicalbigg 2 m ( F cos + mg sin  k N ) D 5. v = radicalbigg 2 m ( F cos  mg sin  k N ) D correct 6. v = radicalbigg 2 m ( F cos  mg sin ) D 7. v = radicalbigg 2 m ( F cos + mg sin ) D 8. v = radicalbigg 2 m ( F cos  mg sin + k N ) D Explanation: The work done by gravity is W grav = mg D cos(90 + ) = mg D sin . homework 15 YOO, HEE 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 ....
View
Full
Document
 Spring '08
 Turner
 Force, Mass, Work

Click to edit the document details