Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Conceptual Question 4.16
[10 points.] An SUV collides with a Mini Cooper convertible (of much smaller mass). No one is hurt in this accident. During the collision, is the force exerted on the Mini by the SUV greater than, equal to, or less than the force exerted on the SUV by the Mini? Explain your reasoning using the properties of forces and of Newton's laws.
Solution and grading rubric:
- p = 10/10:
Correct. According to Newton's third law, the two contact (normal) forces involving the SUV and the car have the same magnitude (but have opposite directions), regardless of their different masses. - r = 8/10:
As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. E.g., recognizes that the two forces have the same magnitude, but has garbled application of Newton's third law, or recognizes applicability of Newton's third law, but does not realize that the two forces have the same magnitude. - t = 6/10:
Nearly correct, but argument has conceptual errors, or is incomplete. May state that the forces have the same magnitude, but due to reasons other Newton's third law. - v = 4/10:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. E.g., does not recognize that the two forces have the same magnitude, but still attempts to apply Newton's laws in some manner. - x = 2/10:
Implementation/application of ideas, but credit given for effort rather than merit. - y = 1/10:
Irrelevant discussion/effectively blank. - z = 0/10:
Blank.
p: 12 students
r: 4 students
t: 7 students
v: 19 students
x: 0 students
y: 0 students
z: 0 students
A sample of a "p" response (from student 6154) is shown below:
A sample of a "t" response (from student 1397) is shown below:
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