Question

In a physics lab, students take a long piece of string and cut it into two unequal pieces. One piece is used to suspend a large weight. The second piece is tied to the bottom of the weight as seen in the diagram below. Student 1 predicts that the upper string will always break first since it has to support the weight and the applied force, while Student 2 disagrees and predicts that the shorter piece of string will always break first if you pull slowly but with enough force to exceed the strength of the string.
(a) Which aspect(s) of Student 1’s reasoning, if any, are correct? Explain your answer.


(b) Which aspect(s) of Student 2’s reasoning, if any, are correct? Explain your answer.


(c) Which aspect(s) of both Student 1’s and 2’s reasoning, if any, are incorrect? Explain your answer.

(d) The experiment is performed and both students are surprised to learn that whether
the upper or lower string breaks first depends on whether you pull slowly or with a
sudden pull. Resolve the two lines of reasoning of Student 1 and Student 2 by
explaining the results of the experiment in a clear, concise paragraph.

Answer 1

Answer:

(a) The aspect of the upper string supporting the weight and the applied force

Student 1 is correct because the upper string is the source of support of the large weight and the force applied to the short string reacts at the support of the long string

(b) The aspect of Student's (2) reasoning that is correct is that the shorter piece of string will always break first, however, the statement is only true for sudden pull due to the increased force experienced by the shorter string from a more rapid change in momentum

(c) The aspect of Student 1's statement that is incorrect is the that the upper string will always break first

The aspect of Student 2's statement that is incorrect is the that the shorter piece of string will always break first

(d) A string will break when subject to a force equivalent to its breaking force. The force experienced by the string increases as the rate of pull (suddenness) increases and the suddenness increases inversely with the length of the string, as such the shorter lower string will break first from a sudden pull before the force of the pull is completely transmitted to the upper string. Whereby the lower string is slowly pulled, the force is evenly transmitted to the upper string which is then taking up the load of the weight and the applied force together and is likely to break first

Explanation: