Errors in Jan 2011 version of Ruina/Pratap
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Make money if you are the first to find an error: $1.00 for math errors, $5 for real errors or things that need deep fixing (with suggestion about how to fix). How?: Subject line in email: TEXT ERRORS. Then list like the Known Errors below, (XX are your initials), e.g.,

Sect 13.2, pg 642, paragraph above "More about pendula". -XX 2/5/11
In the argument of the exponentials change    gt/l     to     +- sqrt(g/l)t.

Known Errors
We keep track of typos, case and tense mismatches, mising closing parentheses, spelling and grammatical errors, etc, but don't list them all here. The errors below are generally more serious.

* = an appropriate repair has already been made in the source file
! = non-trivial error, readers should note.


! Font problems. The printed book, and the pdf of it as viewed on a few computers, has some font problems. Example: problem 9.3.10 part f. It should read      x hat = ... (that's x with a hat on top). This means that hat's are probably missing here and there in the whole printed book (and pdf as viewed on a few computers). Please let me know any places you see this and I will post them. -Luke Strauss 2/15/11. A new book file was posted on 2/15/2011 at 8:35 PM that seems to work better on most computers. Please download the new version.

p.55 - sample 2.7. -MM March 2012
'does the net force double' is ambiguous between the net force vector and the net force, which can be understood as the magnitude of the force vector.
recommend rewording question to : 'does the net force vector double' -MM March 2012

p.58 box 2.2 should be 2.3 -MM March 2012

! page 61, section 2.2, example called "closest point", last equation. -K 3/15/11
As written there is a vector plus a scalar. The second term in the sum should be multiplied
by the unit vector defined by the fraction (rB - rA)/|rB - rA|. Its a projection times a unit

page 67, section 2.2, paragraph starting "Study of fig. 2.40" -K 3/15/2011
Delete "you could".

p. 68, box 2.5, 7: something wrong with this equation -MM March 2012

! page 68, box 2.5 "Uses of the cross product" -K 3/14/2011
Item 4, distance between two lines. The cross product expression, in parethesese,
needs to be divided by its magnitude. The distance between two lines is a unit vector orthogonal
to both lines, dotted with any vetor from one line to the other. Actually,, the magnitude of that result.

page 70, Fig 2.42. - k 3/15/2011
Maybe also mention the 3-finger heuristic for direction of cross product. First vector is
pointer, second is middle finger, thumb is cross product.

page 76, Sample 2.17 -K 3/15/2011
Needs some mention like "angle CCW from a to b" and also of the right hand rule.
Otherwise there is no reasoning for why we have the k direction as opposed to the -k direction.

page 87, 'moment about an axis' - result should be -41/sqrt(2), not -14/sqrt(2) -MM March 2012

p. 97, fig 2.66: should be "walk O to C via D" -MM March 2012

superscript of fig 2.55 is L, should be perpendicular symbol. -MM March 2012

*Sect 3.1, pg 159, paragraph under the title "String, rope, wires, and light chain". -RAC 04/03/12
In the highlited text under this paragraph, note 7 is called, but is missing in the text.

page 209, Sample 4.9 - K 3/19/2011
Change      R-     to     R=    .

page 227, section 4.4, last paragraph. -K 3/21/11
A jumbled sentence therein should read:
"On one side of the cut a force and moment act. On the other object,
on the other side of the cut, the opposite force and moment act."

pg 431. d'Alembert not D'Alembert. Also, in 2 of 10 uses the spelling is wrongly written
as d'Alambert instead of d'Alembert.

Section 9.3, pages 459 and 472. - G Metzler 3/1/2011
Usage of   'natural frequency' and 'angular frequency' don't match Wikipedia. Reversed?

Sample 9.27, page 503 - J. Tashman 3/1/2011
Change answers from    1.9N  and 190N     to      190N  and   19000N.

!Problem 9.1.17, page 521. - M Coleman, Feb 8, 2011
Units are not sensible. Should replace    t     with    t/s   in both equations.

!Problem 9.5.9b MJM - 2/19/11
In the solution manual the term     (mB + m) / m     should be changed to     [ (mB + m) / m ]^2.

!Sect. 11.1, pg 584, Power Balance equation. - M. Coleman, Feb 8, 2011
Change       the vector v_i^2 (nonsense)       into          the scalar v_i^2.
(Or into  the    vector v_i    dot    vector v_i).

Sect 11.2, page 592, figure 11.9. - N. Sen, March 20, 2011
In the first part of the figure the left mass is mass 1, not mass 2.

Sect 14.4, page 819, Sample 14.26 - J. Tashman 4/19/11
Problem statement should have mu = 0.2 (instead of 0.12)
to be consistent with the numerical answer at the bottom.

!Sample 14.15      M Coleman (5/1/11)
Third line from bottom of pseudo-code is:
Change        rpy = rcy + l*cos(q*t)
To                rpy = rcy + l*cos(w*t)

!Sect. 15.3, pg 872, the sentence just before the figure - Roberto Padovani, Feb. 1, 2011
Change      absolute      to       relative
Change      relative       to        absolute

!Sect 16.1, pg 931, Sample 16.8, eqn 16.13 and after. - M Colemean 4/24.11
Equation 16.13 and all that follows is incorrect. The IC's were applied incorrectly to get the
coeff's A and B. Should be
              A =  R_0* lambda_2/(lambda_2-lambda_1) and
              B = -R_0*lambda_1/(lambda_2-lambda_1)
which changes the rest of the solution.

Fig. 16.41 on page 942 -Neil Sen 5/10/11
the force vector for the weight of the wedge reads "mg" when it should be "Mg"

!Sect 16.3, pg 954, in eqn just after "These terms are all we need to evaluate the 4
terms in Eqns. 16.53 and 16.54.": M- Coleman 4/26/11
(-m_2*g j_hat)    should be     (m_2*g i_hat).

!Page 927, sample 16.6 -S Lee 5/9/11
As is, we put in the R0 value for k, which is wrong.
We put in 0.3m and should have put in 0.05m, which will give you -13.63m/s^2*e_r + 3.6m/s^2*e_theta as the acceleration.
the net force then becomes: (-1.36*e_r + 0.36*e_theta)N, with magnitude of 1.407N.
Also, just after "substituting..." the R*theta^2 and 2*R*theta should have their respective "dots". R*theta_dot^2 and 2*R_dot*theta_dot.

Editorial issues

m for mass and m for meters, how to distinguish? (now uses script and roman).
Mike suggests trying to subscript most masses (e.g., m_e for mass of earth).

s for distance and seconds, how to distinguish? (now uses script and roman).

Add essay about magnitude of vector vs scalar part. Often it is nice to think of negative "speed" or negative "force".

Chap. 14.2 needs more problems. Most of the general motion problems are
pure rolling in Ch. 14. - M. Coleman.

Make an end-of-chapter problem by adding friction to sample 16.16 and
16.17. - M. Coleman

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