# Search results

1. ### Basic probability, conditional probability

Is the intersection probability such as P(E ∩A) correctly calculated? I was googling about that thing and I just became more confused by the fomrula I found. Something like "the general multiplication rule of probability" The examples that we had in class were mostly about simple things like...
2. ### Basic probability, conditional probability

Homework Statement what is the probability that a component which is still working after 800 hrs, will last for at least 900hrs Homework Equations conditional probability P(E|A) = ( P( E ∩ A) ) / ( P(A) ) The Attempt at a Solution Im just checking my own understanding if this problem...
3. ### Confused about integrating acceleration to get velocity

So, when you have the so-called dummy variable... I don't get it why it is called dummy variable? I thought that the variable matters because the definite integral should be like, essentially... the limit of the Riemann sum. So.. I suppose if we don't do the actual limit, but just think about...
4. ### Confused about integrating acceleration to get velocity

ok, but mathematically speaking the integral function ##v(t)= t^2+t##is defined in the real numbers, I suppose it makes more sense to think about the thing from the physics point of view though, like you suggested the function itself does go under the t-axis such as v(-0.5)=-0.25
5. ### Confused about integrating acceleration to get velocity

Homework Statement acceleratin as function of time ##a(t)= 2t+1## we know that v(0)=0 and s(0)=0 find v(t) find v(5) find s(t) find s(3) and I was thinking about also what happens when t is negative number, is it possible to find also v(-2)? what about s(-3)? Homework Equations integration...
6. ### Vector dot product and parallel vectors

I see, thanks for your input though. Studyin math always seems to bring out new tidbits like this. Especially studying math in English (not my native language):smile:
7. ### Vector dot product and parallel vectors

not really. I was taught about this dot product thing on Wednesday. I was just a little bit confused by the quote in the textbook which discussed a general casse of vectors a and b. There was the statement that if a and b are parallel, then it follows that the angle is zero... But that...
8. ### Vector dot product and parallel vectors

Homework Statement show that points P, Q and R are in a straight line P (1, -3, 4) Q ( 2, 2, 1) R (3, 7, -2) and find the vectors ## \vec{PQ} ## and ## \vec{QR} ## Homework Equations The Attempt at a Solution In proving that the points are in a straight line, we might be able to use dot...
9. ### News Studying completely on tablets and devices...

I really liked taking pictures of the teacher's scribblings on the blackboard during physics classes. It's not quite the same as doing all thw studying on electronic devices but taking snapshots witj smartphone during class does free up some effort on your part to better focus on the lecture I...
10. ### 3-D vectors forces exerted upon a mast

please elaborate if you have the time my brain is about to freeze at this point with this exercise. I suppose with some more effort I could solve the system of Equations manually, but... I think even my textbook used an equations solver in some of the worked examples. I was reading my...
11. ### 3-D vectors forces exerted upon a mast

A simpler solution would be welcome if anybody has got this figured ouit... I can ask the teacher in a couple of days if this was incorrect or correct...
12. ### 3-D vectors forces exerted upon a mast

part C give the form of the force vector ## \vec{r_3} ## when its magnitude is 800 N the cable R_3 is parallel to the force vector r_3 cable R_3 is of the following form ## R_3 = x*\hat{i} + y* \hat{j} - 30\hat{k} ## length of the cable is unknown and was not part of any information that...
13. ### 3-D vectors forces exerted upon a mast

small r vectors are force vectors, where as capital R vectors are really just the lengths of the cable which goes from the top of the mast to the ground.(i.e. xy plane) My interpretation was that the arrows are the force vectors because they are "floating around" with no endpoint. Where as the...
14. ### 3-D vectors forces exerted upon a mast

Homework Statement The thick arrows represent forces exerrted upon the mast Let ## \vec{r_2} = ~~the~~ longer~force~ vector~~## ## \vec{r_1} = ~the ~shorter ~force ~ vector## correspondinly ## \vec{R_2} = cable ~~2## ## \vec{R_1} = cable~~1 ## r_1 is in the same direction as R_1 r_2 is in...
15. ### Constructive interference with sound -- word problem

After some tabulating of values and some wolfram alpha calculations I used my formula ## \Delta X = n * \frac{\lambda}{2} ## where ## n = [2, 4, 6, 8 ...] ## ## \sqrt{a^2+11.56} -a = n * \lambda / 2 ## ##choose~~ n = 2 ; a = 5m ## first maximum ##choose~~ n= 4 ; a \approx 1.7151m ## second...
16. ### Constructive interference with sound -- word problem

quite so... I came to the same realisation after I started visualizing the process by which the difference of the length c, and length a, of the triangle changes. When the length a = AO shrinks, then that means that the result (the difference ##\Delta X## = (c-a) is going to increase and...
17. ### Constructive interference with sound -- word problem

well it looks like we have formula such as ## \Delta X = n*\frac{\lambda}{2} ## n=4 ## \leftrightarrow \Delta X = 2.093 ## from the triangle we know that length c = BO = hypotenuse it is going to vary length a = AO = varying side length AB = fixed value at 3.4m ## c =\sqrt{a^2+11.56} ## we...
18. ### Constructive interference with sound -- word problem

I did get the lengths for direct path (5m = line from A to O = let's call it ##d_1##) in the first sound maximum case. But I was wondering what would be the length of the direct path for the second sound maximum ##d_2##. That is to say the length at which the second maximum occurs along the...
19. ### Constructive interference with sound -- word problem

1.) If you wanted to know, how would you get the distance travelled for each signal from speaker A -> observer and from speaker B->observer in the case of the second maximum. Is there enough info? for sure it is known what the ## \Delta x ## will be, but the individual lengths AO and BO (A to...
20. ### Constructive interference with sound -- word problem

its going to be constructive interference of some kind. But I dont know if its one wavelength which is the delta distance. Or is it two times the wavelength which is the delta distance.
21. ### Constructive interference with sound -- word problem

Homework Statement [/B] I was little bit confused about interference word problem in an old physics exam. I managed to ace the problem in the exam, by applying a little bit common sense to it, but I feel like I didn't understand the concept of the interference completely. (Loud)speakers A and...
22. ### Today I Accomplished

I refreshed my memory about trig equations and did homework. I was rather proud of my information-seeking and self- learning efficiency because our class went quite fast through trig equations. But during the weekend I managed to do all my homework. So that was something I accomplished yesterday...
23. ### Resonance box with tuning fork, standing wave

Homework Statement There is a resonance box with one end cloesd and the other end open. The box reinforces the sound of the tuning fork. That sound has frequency of 440 Hz sound velocity is 340 m/s a.) What is the basis of the phenomenon in question? b.) define the shortest possible length of...
24. ### How do I not worry about my test score after turning it in?

I had a similar experience with a physics exam about wave motion. I was bothered about a frequency problem I had done in the exam. I was supposed to find the second lowest frequency for a standing wave. During the next day after the exam. I woke up in the middle of the night in my bed and...
25. ### Find two lowest frequencies standing wave

yea standing waves are easier to visualize when they are transverse standing wave. Isn't it just the sum wave? But this one in our example was supposed to be longitudinal standing wave. Do you know or have any good studying materials for these, like an animation or something?
26. ### Find two lowest frequencies standing wave

For the guitar string case. The string is fixed at the ends, but when finding the 2nd harmonic from the base freq, you're still supposed to add the third node into the middle portion. And Then add correpondingly add another antinode. But you're still saying that in the guitar string, it does...
27. ### Find two lowest frequencies standing wave

Homework Statement A metal bar is attached into a vice in the middle. Bar is hit with a hammer creating a longitudinal standing wave find the two lowest frequencies. Bar's length l= 3m wave velocity = 5100m/s Homework Equations wave equation ## v = \lambda * f ## The Attempt at a Solution...
28. ### Harmonic wave in a string

I had to use a physics dictionary to translate some of the words, but that does sound just about right. Our teacher gave us an answer that 1.3 milliseconds is one correct answer Indeed the question did originally state that any one correct answer will suffice. But the idea with the trivial...
29. ### Harmonic wave in a string

Im not so sure anymore about that. I may be wrong, though. The thing which seems to happen in the problem is that in the beginning if there isnt any wave anywhere. Then the "pulse " travels up to the location at 2m. Wouldn't that first pulse be the origin point of A itself?... so you're...
30. ### Harmonic wave in a string

you mean that... in the first loop of the wave (in the distance between A and B) there is a node point. When that node point hits the B then B will be at equilibrium