hw 15 - homework 15 HETTIGER, CHRISTOF Due: Feb 23 2008,...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: homework 15 HETTIGER, CHRISTOF 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 = + k N D 5. W = 0 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 D cos 2. W = N D 3. W = ( mg cos + F sin -N ) D 4. W = ( N + mg cos + F sin ) D 5. W = ( N - mg cos - F sin ) D 6. W = 0 correct 7. W = N D sin 8. W =-N 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 cos + mg sin - k N ) D 2. v = radicalbigg 2 m ( F cos - k N ) D 3. v = radicalbigg 2 m ( F cos + mg sin ) 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 sin + k N ) D 8. v = radicalbigg 2 m ( F sin - k N ) D Explanation: The work done by gravity is W grav = mg D cos(90 + ) =- mg D sin . homework 15 HETTIGER, CHRISTOF Due: Feb 23 2008, 4:00 am 2 The work done by the force F is W F = F D cos . From the work-energy theorem we know that W net = K , W F + W grav + W friction = 1 2 mv 2 f ....
View Full Document

Page1 / 5

hw 15 - homework 15 HETTIGER, CHRISTOF Due: Feb 23 2008,...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online