EM120 – StaticsHandout-Writing Assignment Example.docx
Example Problem:
Determine the magnitude of the resultant force FR = F1 + F2 and its direction, measured counterclockwise from the positive x axis.
Assignment:
Describe the steps followed in order to setup and solve this particular problem.
Student Response (Example 1):
The objective of the problem was to find the magnitude of the resultant force vector, Fr, and its direction.
The first step is to add vectors F1 and F2 by putting the tail of F2 to the tip of F1 and then connecting the tip of F2 to the tail of F1 with a line thus creating a triangle. This new line is the resultant vector, Fr. The angle opposite vector Fr is found by adding the complementary angles of F1 and F2. Use the law of cosines to find the magnitude of Fr.
The sine of the angle opposite vector Fr divided by the magnitude of Fr is equal to the sine of the angle opposite vector F2 divided by the magnitude of F2. Solve for the angle opposite F2. To find the direction of Fr relative to the x-axis, subtract the angle opposite F2 from the angle F1 makes with the x-axis.
Example Problem:
Determine the magnitude of the resultant force FR = F1 + F2 and its direction, measured counterclockwise from the positive x axis.
Assignment:
Describe the steps followed in order to setup and solve this particular problem.
Student Response (Example 2):
The objective is to determine the magnitude of the resultant force FR = F1 + F2 and its direction, measured counterclockwise from the positive x-axis. First we multiply the forces by the cosine of the angles to find the x component. Then we multiply the forces by the sines of the angles to find the y component.
We then square the x and y components and add them. Then I take the square root of the sum to find the magnitude of the resultant force. I then use the law of sines to find the angle of the resultant force. To do this I take the sine of 90 over the magnitude of FR and multiply it by the y component. I then take the arcsine of the result, subtract it from the degrees in a circle and this gives me the angle of the resultant force.
Scoring Rubric (Example 1):
Criteria / Full Credit (2 pts.) / Partial Credit (1 pt.) / No Credit (0 pts.)Has the student provided sufficient detail that another beginning Statics student could reproduce the approach to the solution? / Identify sequence by which unknowns are being found. / One necessary step is missing or steps are slightly out of order. / More than one necessary step is missing or greatly unordered.
Variables used in each equation are identified. / Variables used are not identified in one equation. / Variables used are not identified for multiple equations.
Body or particle chosen for FBD is identified (if applicable). / Body or particle for FBD not clearly identified.
Has the student demonstrated an understanding of what is being done in the solution process? / Approach described is fundamentally sound. / One error in the approach or distracting extraneous information. / Multiple errors in approach.
Each equation used is described in words, not with algebra. / One equation described algebraically. / Multiple equations described algebraically.
Is the description written such that an expert can understand what the student means? / Description begins with the objective(s) of the problem. / Description does not begin with the objective of the problem.
Pronouns have clear meanings (each sentence is easily understandable). / One or two sentences are not clear. / More than two sentences are not clear.
Is the description focused on the approach to the solution of this problem, not the specific numbers of the solution? / No problem-specific quantities are used in the description. / One problem-specific quantity is provided in the description. / More than one problem-specific quantities are provided in the description.
Details are provided about solving this particular problem. / Description is about how to solve this type of problem in general.
Is the assignment formatted according to guidelines given? / Description no longer than ¾ page typed using font size and paragraph spacing indicated. / Description more than ¾ page, but less than 1 page. / Description more than one full page typed.
Vectors are boldfaced, scalars are italicized. / One or two vectors/scalars are not properly formatted. / More than two vectors/scalars not properly formatted.
No figures are present. / One or more figures are present.
Scoring Rubric (Example 2):
Criteria / Full Credit (2 pts.) / Partial Credit (1 pt.) / No Credit (0 pts.)Has the student provided sufficient detail that another beginning Statics student could reproduce the approach to the solution? / Identify sequence by which unknowns are being found. / One necessary step is missing or steps are slightly out of order. / More than one necessary step is missing or greatly unordered.
Variables used in each equation are identified. / Variables used are not identified in one equation. / Variables used are not identified for multiple equations.
Body or particle chosen for FBD is identified (if applicable). / Body or particle for FBD not clearly identified.
Has the student demonstrated an understanding of what is being done in the solution process? / Approach described is fundamentally sound. / One error in the approach or distracting extraneous information. / Multiple errors in approach.
Each equation used is described in words, not with algebra. / One equation described algebraically. / Multiple equations described algebraically.
Is the description written such that an expert can understand what the student means? / Description begins with the objective(s) of the problem. / Description does not begin with the objective of the problem.
Pronouns have clear meanings (each sentence is easily understandable). / One or two sentences are not clear. / More than two sentences are not clear.
Is the description focused on the approach to the solution of this problem, not the specific numbers of the solution? / No problem-specific quantities are used in the description. / One problem-specific quantity is provided in the description. / More than one problem-specific quantities are provided in the description.
Details are provided about solving this particular problem. / Description is about how to solve this type of problem in general.
Is the assignment formatted according to guidelines given? / Description no longer than ¾ page typed using font size and paragraph spacing indicated. / Description more than ¾ page, but less than 1 page. / Description more than one full page typed.
Vectors are boldfaced, scalars are italicized. / One or two vectors/scalars are not properly formatted. / More than two vectors/scalars not properly formatted.
No figures are present. / One or more figures are present.
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