# Homework Help: Schaum's Outline for Engineering & Science errors!

1. Mar 17, 2006

### johngatlin

I'm hoping that at least one of you have read/worked with this book and noticed that there are blatant errors in the solutions he gives to his problems. How am I supposed to check and see if I'm going about it correctly if I cannot verify my answer in the end? It's my only "text book" for the class and I'm on a break, trying to get ready for a test on Tuesday. I'm in an odd situation because there seems to be numerous errors/irrevelant procedures in these chapters and now I'm not sure what to trust.

My test is going to cover many topics dealing with Rotational Dynamics:

1) Relating Linear and Rotational Variables (piece of cake)
2) Rotational Kinetic Energy (Got it down for itself, but why do I now have to combine it with linear KE for problems such as dealing with a mass hanging from an atwood machine? Why didn't I take this into account before?)
3) Moment of Inertia Calculations (I'm somewhat versed in using them if they are given to me, but can I figure for a non-given/continuous object without calculus?)
4) Parallel-Axis Theorem (I'm very hazy with this, as in "why?")
5) Torque (I've got all of the equations down, but I have questions about the perpendicular lever arm)
6) Rolling (easy enough with KE)
7) Angular Momentum (I only have to deal with Conservation (no external torque?))
8) Rotational Equilibrium (I'm fine with straight things such as sticks on scales with weights, but other than that I'm gone. i.e. angles (ladders, planes), maximum overhangs, etc.)

I don't have to know about rotational work and power, the perpendicular-axis theorem, and precession.

So, my question is: Is there any place that has addressed this problem and has posted corrections? Have any of you who have worked with the book noticed this?

If no, or if it doesn't help me, is it OK if I post a plethora of questions not exactly looking for numerical answers but rather the reasoning behind all of this?

Thanks,
Drew

This might need to be moved to introductory physics, sorry.

Last edited: Mar 17, 2006
2. Mar 17, 2006

### Valhalla

I used this book and yes there are lots of calculation errors in the book. This was not my only book for my Physics 1 course though. Usually these are just for supplementary information. Did you not buy the physics textbook? If you didn't I highly suggest getting that. The theory given in the schaum's is a refresher. It hits key points but doesn't give reasons why. If this is your book for the class, I suggest buying a used physics textbook ASAP from an online source.
As far as the errors in the schaum's I believe most of them were number errors. He punches in wrong numbers or multiplies when he should add, etc. The method is what is important. Values are trivial. If you can understand the method to get a solution then your set. (Although we all know how much arithmetic errors can kill us in these classes!!)

3. Mar 17, 2006

### johngatlin

Here's an example of something I'm confused about. We worked this out in class a while ago, but I've forgotten what we did.

Say you have an atwood machine (pulley) with mass (M) and radius (R). You have a block of mass (m) hanging from one side of the pulley. Find the linear acceleration (a) of the block.

Ok. So first guess is to use F=ma. Bingo. Second, plug in the forces. We have the weight of the block (mg) and Tension. So..

mg - T = ma

Now, what I substituted for T doesn't make sense to me. It was (.5)(M)(a). I guess we got this from Torque = I (alpha) and plugged (T)(R) for Torque, then did a bunch of algebra and winded up with (.5)(M)(a) being Torque. Then we solved for (a), a=(mg)/(m+(.5)M), and all was gravy.

But I don't understand why the mass of the pully is revelant to the Tension and the mass of the block isn't. It used to be that the mass of the block was all that mattered, and now it's thrown out of the picture? The Tension being subject only to the mass of the pully and the acceleration?

Last edited: Mar 17, 2006
4. Mar 17, 2006

### johngatlin

I guess that explains why Schaums hasn't been all that great. My teacher didn't supply/tell us to get anything else so I'm lost in that department. Do you have any textbooks to recommend?

And yeah, arithmetic is the worst. Absolutely. That and pretty much everything up to Calculus I've long forgotten; even Calculus sort of, which explains why I don't get his reasoning, even though they're simple enough integrals.