Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Problems 7.42, 7.49
[20 points.] A 0.200 kg cart collides elastically with a 0.700 kg cart that is initially at rest. If the 0.200 kg cart was traveling in the +x direction at 1.40 m/s before the collision, what is the velocity (speed and direction) of the 0.200 kg cart after the collision? Show your work and explain your reasoning.
Solution and grading rubric:
- p = 20/20:
Correct. Applies both momentum conservation and kinetic energy conservation for this elastic colllision, and finds both the magnitude and direction of the final velocity of the 0.200 kg cart. - r = 16/20:
Nearly correct, but includes minor math errors. - t = 12/20:
Nearly correct, but approach has conceptual errors, and/or major/compounded math errors. At least applies both momentum and kinetic energy conservation. - v = 8/20:
Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner. Typically only attempts momentum conservation. - x = 4/20:
Implementation of ideas, but credit given for effort rather than merit. - y = 2/20:
Irrelevant discussion/effectively blank. - z = 0/20:
Blank.
Grading distribution:
Sections 70854, 70855
p: 16 students
r: 1 student
t: 16 students
v: 8 students
x: 1 student
y: 1 student
z: 0 students
A sample of a "p" response, applying both momentum conservation and (the vector form of) kinetic energy conservation, and then methodically feeding the answers back in to verify that the two conservation laws were satisfied (from student 7503):
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