Introductory Physics I: Mechanics and Wave Motion Midterm II

Less polished (i.e. handwritten) questions that are similar to the kind I would ask on the second midterm.

Questions

Practice exam questions

Answers

Practice exam solutions

Warning: this was a 3-hour exam and covered slightly more material than we have seen so far.  In particular, you are not responsible for center of mass problems like the last one on this exam.  Yet. 

This was a hard exam.

Questions

Past midterm 2 questions

Answers

Past midterm 2 solutions

Preamble

This is a lot of problems.  I do not expect you to complete every one of these.  I do suggest that you attempt each one.  If you are confident you can do a problem, skip it.  Otherwise, rough out a solution by writing down a system of equations and thinking through how you would solve them.  Check against the posted solution to see if your thinking is correct, but you probably don't need to do all the algebra unless your approach is different from the solution's and you're unsure whether they concur.

Questions

Friction: 5.45, 5.66, 5.85, 5.92.  Many of these can be solved with Newton's laws or with conservation of energy.  The latter is usually easier.

Pulleys: 5.65.

Energy: 6.78, 6.85, 7.44, 7.48, 7.65, 7.73.

Momentum: 8.28, 8.66, 8.69, 8.76, 8.79, 8.84, 8.88.

Optional: Rotation: 5.53, 5.54, 5.104, 5.115.

Answers

Midterm 2 practice problems solns

Date and Time

Midterm II will be given Thursday Nov 13 from 7-9 PM in Merrill 1.

Topics

The material in Physics 16 is inherently cumulative: it is almost impossible to write an exam that does not draw on material from the beginning of the course.  Although you may need to use material from the first midterm, I will try to focus the second midterm on later topics.  In particular, the second midterm will cover conservation of energy and momentum (Chapters 6-8, not including center of mass and rocket propulsion), as well as friction (end of Chapter 5). 

Crib sheet

You may bring your crib sheet from the first midterm and an additional two sides of handwritten notes prepared by you personally. 

Review session

I will use the normal lab times (Monday and Tuesday afternoons) for informal review sessions.  In addition, since there is no problem set due next week the normal evening problem session will be converted to a review session and (exceptionally) it will be moved to Tuesday evening. 

Review problems and practice exam

will be posted here over the next few days

Particular problems I observed in the first exam:

1. When I say "use units" I do not simply mean "append a unit to anything you've calculated or I'll take some points off".  Units are actually very useful – especially if you do your calculations with variables instead of with numbers.  A quick check of the units in your final formula will reveal most algebra errors.  You can then go back and check units at intermediate steps: a dropped factor of m, for instance, will show up as a missing unit of kg in all the intermediate steps from the point of the error onward. 
2. Force are vectors.  You cannot add the x component of one vector to the y component of another; in fact, (unless you're doing graphical vector addition) to add vectors you always need to find components and then add together x components and y components separately.
3. Newton's 2nd law (F_net = m a) has two sides.  Some people did a good job with the LHS (adding the force vectors) but didn't think hard enough about the RHS.  Typically, this involved incorrectly assuming that some acceleration was zero.  When an object is not moving, its acceleration is zero.  But an object undergoing circular motion, or being pushed on by an outside force, does not have a zero acceleration; there is often one particular component of its acceleration that is zero, but you must identify that component carefully.  If you set up your axes wrong, you will assign zero acceleration to a direction that is not, in fact, zero.
4. There are only 26 letters in the English alphabet.  Even throwing in Greek (and occasionally Hebrew), we do not have enough letters to give a unique letter to every object in physics.  Distinct and totally different concepts often end up with the same letter.  For instance, both tension in a rope and the period of revolution are labeled T.  You need to have in mind the meaning of every variable that you use so that you don't conflate the period T with the tension T.  If both appear in the same problem, the safest thing to do is relabel one of them (for instance, call the tension F instead of T).