# HW2 - PHYS125 Homework Assignment #2 Grading Rubric Stage 1...

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PHYS125 Homework Assignment #2 Grading Rubric Stage 1 2 points each Problem 1, 3.47, Problem 4, 4.29, 4.50 Stage2: River Race ~1 point for accurate sketch ~2 points for angle determination (part a) ~2 points for vector addition to get G’s velocity (part b) ~1 point for correct time (part b) ~2 points for vector addition to get S’s velocity (part c) ~1 point for correct time (part c) ~1 point for who won the race…. Gordon! Stage 3: Exiting the freeway Motion diagram: ~1 point drawing ~1 point draw/label velocities ~1 point draw/label acceleration Force Identification ~1 point circle the car ~1 point normal force perpendicular to plane ~1 point gravity perpendicular to horizontal ~1 point friction/brakes goes up the plane Free Body Diagram ~1 point for coordinate system ~1 point for decomposing all vectors ~1 point for Fnet

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Stage 0 Solutions These are not to be tuned in, not will you receive credit for working them. Their aim is to further familiarize the student with the relationships and gain added practice. Practice Problems: 3.1, 3.5, 3.7, 3.15, 3.19, 4.1, 4.3, 4.5, 4.9, 4.13, 4.21 More Good Problems: 3.37, 3.39, 3.41, 3.45, 3.49, 4.25, 4.27, 4.37, 4.45, 4.49 3.1. Solve: (a) If one component of the vector is zero, then the other component must not be zero (unless the whole vector is zero). Thus the magnitude of the vector will be the value of the other component. For example, if A x = 0 m and A y = 5 m, then the magnitude of the vector is 22 (0 m) (5 m) 5 m A =+ = (b) A zero magnitude says that the length of the vector is zero, thus each component must be zero. 3.5. Visualize: Solve: (a) To find AB + r r , we place the tail of vector B r on the tip of vector A r and then connect vector ’s A r tail with vector ’s B r tip. (b) To find , we note that r r () A BA B −=+− rr . We place the tail of vector B r on the tip of vector and then connect vector tail with the tip of vector A r ’s A r . B r 3.7. Visualize: The figure shows the components v x and v y , and the angle θ . Solve: We have, sin40 , y vv =− ° or 10 m/s sin40 , v ° or 15.56 m/s. v = Thus the x -component is cos40 (15.56 m/s ) cos40 11.9 m/s.
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## This note was uploaded on 06/20/2008 for the course PHYS 125 taught by Professor Mutchler during the Spring '08 term at Rice.

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HW2 - PHYS125 Homework Assignment #2 Grading Rubric Stage 1...

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