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  1. J

    Confused with the answer<> seems correct buttht's wrong wrong?

    Are you sure that your solution doesn't satisfy those equations? When you take the square root of a number, how many solutions do you get?
  2. J

    'Simple' Optimization Problem

    What makes you uncomfortable about the answer you got? Would it make you more comfortable to compare the volume if the height were slightly above or below the height you calculated to the volume you got?
  3. J

    Challenging Momentum of Collision Problem

    There is more than one way to solve the first part of a problem. One way, which you may or may not have covered in class yet, is using the work-energy theorem and equating the change in kinetic energy of a car (which is a function of its initial velocity) with the work done by friction...
  4. J

    Confused about the wording of this probability problem

    I think the problem means that there are 10 unique pairs of gloves in the drawer and X is the number of pairs of gloves after randomly choosing 6 individual gloves. So one possibility is that you chose 6 gloves and none of them pair up, meaning that you have 0 pairs (X=0). Another possibility...
  5. J

    Separation of variables help

    You've done the calculus correctly, now you need to do a little algebra. Hint: what's e^(-ln x)?
  6. J

    Intro projectile motion

    If the bullet had an initial muzzle velocity of 0 coming out of the gun, how high would it go? You are given how high the bullet goes and that it is traveling straight up (against gravity). You also need to realize that the bullet's velocity at its highest point is 0. With that information...
  7. J

    MATLAB Problems integrating in a for loop in Matlab

    Your syntax for 'for' isn't right - it should be: for C1 = 1:moments to do what you want. Writing it the way you did only executes the loop once (with C1 = 1).
  8. J

    Simple Kinematics problem.

    The distance you've calculated (for part a) is how far Andrew would have driven in 3.4 seconds if he decided he didn't care about the fox and didn't step on the brakes. At the moment he steps on the brakes, he is going 75 km/hr, but 3.4 seconds later, he is going 0.0 km/hr (he has stopped)...
  9. J

    Graphite vs maple bridge on a cello

    Hi - As a disclaimer, I'll admit up front that I don't know the answer to your question, but I thought it was interesting since I've never used a graphite bridge before. It sounds like you've already started working on the bridge, so if you couldn't find a luthier to work on it for you, you...
  10. J

    MATLAB Need help creating a recursive script in matlab that can do this:

    This should do it: S = sum((1:n).^2); (1:n) creates an array of integers from 1 to n the .^2 squares each element and the sum() function does what it says.
  11. J

    Help with MATLAB problem

    It looks like everything is okay except for your acceleration value - why is your equation for acceleration -g/m? If you look at your data, you will see that the object does move up before it goes down as it should. You have a typo in your 'Relevant Equations' section (what you have for...
  12. J

    Spring Constant of car

    Bearbull24.5, I believe you solved for the frequency incorrectly (when you solved for w as a function of T, did you end up multiplying 2pi by T or dividing 2pi by T; which should you have done)? And further, while you were supposed to divide by 4, you should have an understanding of why that...
  13. J

    MATLAB Matlab GUI: changing multiple lines static text

    Try setting all of your elements as cells (with the braces) so that you end up with a cell array of strings rather than a character array - your error may have something to do with that because with a character array, if A,B,C, etc. cannot have a different number of elements. e.g.: A={'blah...
  14. J

    MATLAB MATLAB tolerance question

    I don't see anything wrong with the way you are doing it. If you want to reduce your two conditions to one condition, you can use absolute value like this: target = 4; % whatever target you want tol = 0.002; % whatever tolerance you want if abs(myVar(i)-target) <= tol . . . or if you'd like...
  15. J

    Slider Crank Problem

    If you know how to solve the problem, you should have an equation for acceleration as a function of theta (you may not know the value of omega, but you know that the angular velocity is a constant). There's no reason you can't plot this function if you scale your y-axis in units of omega^2...
  16. J

    MATLAB Matlab question

    How consistent is your input string? I mean, will it always be N=XX_ so that the number your interested in is always between N= and an underscore? If so, this should work: %Find the position of 'N='... NEIndex = findstr('N=',textString); %Find all of the underscores... uscoreIndex =...
  17. J

    Very simple matlab question

    It's possible t was already defined so that even though that part of your script should work, it is not changing the value of t(11). Try clearing the value first: clear t for i = 1:10 t(i) = i end Alternatively, you can use vectorized code: t = 1:10; This is cleaner, takes advantage of...
  18. J

    Find coefficient of kinetic friction using energy conservation

    Try recalculating the kinetic energy - the number you got is wrong (you didn't square the velocity). Also, when you say that the friction is less than or equal to mu_k*N - it's really just equal (that is, f = mu_k*N). The less-than-or-equal to part comes into play when you are considering...
  19. J

    Average versus mean

    I've always used "arithmetic mean", "mean", and "average" interchangeably - arithmetic mean is probably the least ambiguous (there are different types of means and means are a type of average). The middle value (7 in your example) is the median, not the mean.
  20. J

    MATLAB Matlab ODE problem

    Oh - sorry about that. Have you tried playing with the tolerance? If you relax the default settings on RelTol and AbsTol, maybe it won't require such a small step size. Other than that I'm not really sure - that might just be the best you can do with the complexity of your system.
  21. J

    MATLAB Plot - Radian Scale (MATLAB)

    Yes - you can set where the tick marks are on an axis: This will control where the ticks go (use whatever range you want): set(gca,'XTick',0:pi/2:3*pi/2) (Note that gca returns the handle for the current set of axes) This will control the labels for the ticks...
  22. J

    MATLAB Matlab ODE problem

    You can specify the points for which the solution is found if you give a vector for the tspan argument. So, if you're saying that it's calculating for too many points when you use t = [0 .01], then you can just specify t = (0:.001:.01) or whatever values it is that you want there. I hope that...
  23. J

    Tension in the String of a Pulley System

    I'm sorry JamesEarl, but if 40.4 is not the answer, then I don't know what is. Free-body diagram of m1 yields the following equation: m1*a = T Free-body diagram of m2 yields the following equation: m2*a = m2*g - T the string is inextensible and massless; there are no other components in the...
  24. J

    Basic ideal gas PV=nRT question ( need help fast )

    Well, it's more or less the same reason you had to add 273 to your temperature - the ideal gas law is defined in terms of absolute pressure and temperature. Did you ever go over the difference between gauge pressure and absolute pressure in class?
  25. J

    Tension in the String of a Pulley System

    I don't see anything wrong with your calculation of tension - the fact that you got the same answer looking at either mass should tell you that you got the right answer (and no, negative or 0 tension does not make sense for this problem). I take it you are submitting your answers online -...
  26. J

    A Helicopter

    You're over-complicating things and incorrectly using the formula for force due to air resistance. Drag in that formula is a function of the cross-sectional area of the bucket as seen by the wind - that is information you do not have according to your problem statement - the area of the...
  27. J

    Basic ideal gas PV=nRT question ( need help fast )

    - you are given gauge pressures, but P in your ideal gas law equation is in absolute pressure - you need to convert gauge pressure to absolute pressure (that is, you need to add atmospheric pressure) - check your algebra when calculating n - looks upside down to me... - otherwise there's...
  28. J

    Differential Equations - am I doing this right

    Looks good to me. One way you can check your work is to find dy/dx from your final equation, and verify that you get your initial equation...
  29. J

    MATLAB Exit function in matlab

    try "return" to exit the function - hopefully that is what you are looking for.
  30. J

    MATLAB Matlab problen with reading from files - need help

    Hmm... not sure what's going on. Here's what I did: - I saved the data you just printed out as a file called 'read.txt'. - here, I've copied and pasted from my command window: >> fid = fopen('read.txt') fid = 3 >> a = fscanf(fid,'%e') a = -9.822387897877512e-009...