Welcome to the website of ME 274 for the Fall 2008 semester. On this site you can view blog posts, add your own blog posts and add comments to existing posts. In addition to the blog are links to course material: course information, information on solution videos, exams, quizzes, homeworks and other course-related material. Direct links to the homework solution videos are also available on the left side of this page.


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Aug 29, 2008

Quiz No. 1 - comments on Problem No. 2

In Problem No. 2 of Quiz No. 1, you were asked to find the rate of change of speed (v_dot) from the given velocity v and acceleration a vectors for a point.

Here you need to recall that v_dot is the projection of a onto the unit tangent vector e_t. Note that we used this in several lecture examples (in particular, the examples on pages 11, 12 and 13 of the course lecture notes). Note that the tangent unit vector e_t is in the same direction as v; that is, e_t = v/|v| .
  • One way (not the best way) to find this projection is to find the angle phi between v and a. Then the rate of change of speed is found using v_dot = |a| cos(phi).
  • Another way (a better approach) that was used in class is to use the dot product to find this projection directly: v_dot = a • e_t
Please go over the Quiz No. 1 solution passed out in class (click here for a copy of the solution). Let us know if you have questions.



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