Instructor Guide

Problem Design Features

Randomized Values

Physics LE problems utilize randomization of the numerical values used in the problem. This ensures that each student receives a unique version of the problem. Most problems have approximately 100 unique variations. This prevents plagiarism among students and makes it nearly impossible for students to search online for the answer to a particular problem variation.

Note: Questions from OpenStax High School Physics are comprised entirely of multiple-choice questions. These multiple-choice questions utilize randomization of numerical values appearing in the problem, and randomization of the letter corresponding to the correct answer.

Versatile Problem Behavior Modes

Based upon the desired objective for the assignment or quiz, the instructor can choose how students interact with problems: single attempt only, multiple attempts with no penalties, or multiple attempts with penalties. Many additional custom settings are also available on the Settings: Assignment/Quiz/Simulation page.

Specific Feedback

For all numerical answers, specific feedback is provided to students using sophisticated algorithms which evaluate the following: correct numerical value (within a set tolerance), correct unit, sign errors, order of magnitude errors, and common misconception errors.

Intermediate Problem-Solving Steps

Intermediate problem-solving steps often appear in the question parts that make up a problem and are indicated with a "+" sign in the part header. Getting each part correct before moving on will help students obtain the correct final answer. The Submit Answer button appearing at the end of the problem can be used to submit any completed part of a multiple-part problem, uncompleted parts are ignored and only the completed part is evaluated. As students develop their routine of solving Physics LE problems they should be sure to always submit the answer to each individual part before moving on.

Intermediate problem-solving steps are of the following types and point values:
1) Intermediate numerical values required to obtain the final answer (0.5 points)
2) Input of relevant equations or algebraic expressions (0.25 points)
3) Multiple-choice questions, using text or diagrams, checking for understanding and problem-solving approach (0.25 points)
The final answer is generally assigned a value of 1.0 point.

Numerical Tolerance

The numerical tolerance used in the student answer for most numerical problems is set at ± 2%, however, this value does vary based on the specific problem. If the student's answer is within the numerical tolerance of the accepted answer it will be marked as correct. This value cannot be changed by the instructor as it is built into the individual problem. Experience shows that having one universal setting for numerical tolerance is not a good approach. A number of considerations come into play when deciding what numerical tolerance should be used for a particular problem.

Significant Figures

All numerical problems require students to input their answer using the correct number of significant figures following standard significant figure rules, with some leniency allowed as described below. Students are guided to make any necessary corrections regarding significant figures prior to the grading system evaluating their answer. The vast majority of numerical problems require students to enter their answer using 3 significant figures.

It's important to have some guidance when it comes to significant figures to avoid frustration on the student's part. As an example, consider a correct answer of 1.25 kg. If the student rounds to 2 significant figures instead of 3 and enters 1.3 kg, his or her answer will vary from the correct answer by 4%. In this case the student answer would be marked as incorrect as the answer tolerance is generally set at 2% - 3%.

Because problems contain randomized values, different sets of random numbers can produce answers with a varying number of significant figures when the rules for addition/subtraction are applied. This is of particular concern when multiple-step calculations are involved. For this reason, when a problem solution has multiple steps involving both multiplication/division and addition/subtraction, only the rules for multiplication/division will be employed.

The grading system provides flexibility concerning the use of scientific notation for answers not involving a decimal that happen to have a zero in the final significant figure position. For example, an answer of 150 m/s requiring three significant figures can be entered in scientific notation as 1.50E2 m/s, in addition, entering 150 m/s is also accepted. This approach is used to make sure all variations of a problem place the same requirements on a student, and not require certain students to enter their answer in scientific notation merely based on the random values used in the problem.

For problems involving multiple steps with a series of calculations, the student should carry at least one additional significant figure through all the intermediate calculations and then round the final answer to the proper number of significant figures. Students may find it convenient to input a series of calculations into their calculator at one time and thereby automatically retain extra digits for intermediate calculations. The practice of not carrying at least one additional significant figure in multi-step calculations can create a compounding truncation/rounding error and cause the student answer to fall outside the tolerance limits of the accepted answer.

Units

All numerical problems require students to enter a unit after the numerical value (with a few exceptions such as when entering a ratio). The unit can be typed immediately after the numerical value (with or without a space) in the same input field. The system recognizes equivalent metric (SI) conversions. If a student forgets to include the unit he/she will be prompted to enter it before the answer can be evaluated.

Most units can be typed just as they normally appear in a textbook (e.g., kg, m, s, m/s, km/h, N). The SI unit for acceleration can be entered as m/s^2 or m/s/s. Units are case sensitive and students need to make sure to use the same uppercase/lowercase convention as used in a physics textbook.

Acceleration Due to Gravity Numerical Value

Physics LE problems utilize a value of 9.80 m/s/s for acceleration due to gravity at the earth’s surface. This value is coded into individual problems and cannot be universally changed.

Careful consideration went into choosing the value to be used for g. There is some debate in the physics education community as to what value should be used for g when considering three significant figures. With the value for g varying over the earth's surface from 9.78 m/s/s to 9.83 m/s/s, some feel 9.81 m/s/s is a good global average. Others feel 9.81 m/s/s creates a misleading picture as to the variation of g and therefore 9.80 m/s/s should be used instead (the same value as that used for two significant figures).

In the end 9.80 m/s/s was chosen due to this value being widely used in college-level physics textbooks. The 0.10% variation between the two values is well below the numerical tolerance used in Physics LE problems. Although it’s recommended students use 9.80 m/s/s when solving Physics LE problems, 9.81 m/s/s can also be used with no issues.