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1. ### Finding the Electric Field

Thanks Siddharth, but if we draw a picture of the two media, geometrically we can conclude that E1t = E2t where E1t=E1-E1n and the same with E2t (I guess you get the picture). I don't see how this would help. Moreover we are dealing with 3-D ( I guess I might have understood it if it was 2-D)...
2. ### Finding the Electric Field

Greetings everyone: I'm trying to solve a problem which requires finding the electric field. I've been pondering on this problem for a while but still no results. The book doesn't give any hints or clues on how to tackle this kind of problems so I would really appreciate some of your...
3. ### Vector Calculus

Hello everyone, I found a random question regarding finding the parametric equations for a tangent line to a space curve and I'm striving to solve it, but no results. I consulted the book but there isn't anything similar. Find the parametric equations for the tangent line to the space curve...
4. ### Solving Vector Calculus Problems in r1(t) and r2(t)

If we get the Unit Tangent Vectors then they are in terms of t. What do we substitute for t to get the value? The point we have is (3,-2,25) ->(x,y,z).
5. ### Solving Vector Calculus Problems in r1(t) and r2(t)

Vector Calculus Greetings everyone, I have a problem: "Consider the curves r1(t)=(t, 1-t, 16+t^2) and r2(t)=(8-s,s-7, s^2) a) At what point do they meet? b) Find their angle of intersection The first part is easy, but I'm encountering some problems with b). To find the angle we need...
6. ### Reflaction of light

Hello to all, I have a physics problem regarding reflection of light. A solid glass cube, of edge 10 mm and n = 1.5 has a small spot at its center. a) What parts of each cube face must be covered to prevent the spot from being seen, no matter what the direction of viewing? b) What fraction...
7. ### Integral from 0 to pi/2 of (x*[sin x]^2) dx

Hello everyone, I was solving an integral, but I am not quite sure for the final answer. If someone has the time, just take a look. Integral from 0 to pi/2 of (x*[sin x]^2)dx I used by parts integration; using u=(sinx)^2 du=2 sinx cosx...
8. ### MATLAB Plotting in Matlab

Hi there, I have a simple function and I want to plot it in MATLAB but i get an error. Maybe someone can help. The function is of the type 1/(X^3 + X^2 +1) I can plot a polynomial but I have no idea about the function above. Thnx
9. ### Electric field on a point charge

For E2 i.e the middle one, I used just 1.01 cm (actually 0.0101 m) and for E3 4cm + 1.01 cm, which is 0.0501 m.
10. ### Electric field on a point charge

Hello guys, I have a question which I think I solved it right but I don't understand why the final answer is wrong. Here's the problem: Consider three charges as shown. k is 8.98755 * 10^9 N m^2/c^2. What is the electric field at a point 1.01 cm to the left of the middle charge? Ans. in N/C...
11. ### Help Needed: Solving Logic Design for Traffic Light Controller

Hello, I am finishing my first semester as an electrical engineer. Thus, we have to do a final project. The problem is that I didn't have to much time in the lab to finish it up, so it is a little bit difficult to solve it theoretically. If anyone can help, I would be grateful. The project...
12. ### Help with a simple project

Hello, I am finishing my first semester as an electrical engineer. Thus, we have to do a final project. The problem is that I didn't have to much time in the lab to finish it up, so it is a little bit difficult to solve it theoretically. If anyone can help, I would be grateful. The project...
13. ### Rotational Dynamics

Can anyone help?
14. ### Rotational Dynamics

Hello, I have a problem dealing with torques and acceleration. I am sure I solved it right but when submitting the answers, I get the response "Incorrect" :cry: The problem: A wheel of radius 2 m, mass 53 kg, and moment of inertia (3/4) (53 kg) (2m)^2 about the center of mass is mounted...
15. ### Conservation of energy of a dart gun

Thanks Parth Dave, In fact the answer was positive. But the second Part is weird. As I told, I applied: mgh = 0.5mv^2 and hence I found v. BUt the answer was wrong. What might be the problem?
16. ### Conservation of energy of a dart gun

:smile: The problems are not as difficult as you think. There's no air friction , but we need to find the energy lost by air friction during ascending. Also no wind or any other factor influencing the trajectory of the dart.
17. ### Conservation of energy of a dart gun

Hey Parth Dave! In fact I need to find the energy dissipated by air friction. So what I think is: Energy = Change in PE + Change in KE = (m*g*h final - m*g*h initial) + (0.5*m*Vfinal ^2 - 0.5*m*Vinitial^2) initial mgh = 0 (h = 0) and final 0.5*m*Vfinal = 0 (v=0) So we...
18. ### Conservation of energy of a dart gun

:smile: In both cases the air resistance is neglected. He said that the exercise doesn't make sense because the numbers come negative. This doesn't happen when I solve the problems. Maybe there's sth wrong in my reasoning? (The professor had different numbers, so maybe there was a typo in...
19. ### Conservation of energy of a dart gun

Hi! I have a two-part problem to solve. I think I solved it but in the class the professor told us that there's something wrong with the exercise. The spring constant of a toy dart gun is 1350 N/m. To cock the gun the spring is compressed 1 cm (0.01 m). The 5g (0.005 kg) dart, fired...
20. ### Work of a Spring: Solve 24 N/m Stretched 0.24 m Problem

:cry: I realized that on Friday night the server had failed because I entered the same answer this morning and amazingly it said "Correct". I don't know what happened; probably a server break down. Anyway thanks a lot for the help.
21. ### Work of a Spring: Solve 24 N/m Stretched 0.24 m Problem

Thank you for the time Doc Al, I wrote the problem exactly as written on the paper. k is 24 N/m and it is stretched 0.24 m from equilibrium. Then the question is; How much work must be done to stretch it and additional 0.072m? (Answer in J) so : W = 0.5*24([0.24+0.072]^2 - 0.24^2)...
22. ### Work of a Spring: Solve 24 N/m Stretched 0.24 m Problem

Thanks Doc Al, I apologize, the work is really positive. That's how I solved it. I have to solve the exercise and submit the answer online. I have only 7 chances. So I tried for the first time using the formula and the distances I wrote on the first post. It said "Incorrect"; than I thought...
23. ### Work of a Spring: Solve 24 N/m Stretched 0.24 m Problem

Anyone can give a hint?
24. ### Position of a spring

The force is negative, so it's -2.8N and you should get 0.08 m. Then you can find the work which is negative too.
25. ### Position of a spring

Hello, I have been having troubles with these springs too but I will try to explain where the problem stands with your exercise. Since the force pulls i.e. is directed +x-axis, it means that the force is negative because the force of spring has to balance the applied force. So it is -2.8N...
26. ### Work of a Spring: Solve 24 N/m Stretched 0.24 m Problem

Hi Diane, For X1 I used 0.24 and as I said for Xf i used 0.24+0.072. I think that the work should be negative since the spring goes toward positive x-axis. I am not really clear with the work on a spring because the chapter on the book was very brief and that other books I have used are...
27. ### Work of a Spring: Solve 24 N/m Stretched 0.24 m Problem

Hello everyone! The problem I have is really easy, but something is confusing me. A spring with spring constant 24 N/m is stretched 0.24 m from its equilibrium position. How much work must be done to stretch it an additional 0.072 m? I used the formula : W = (1/2)*k(Xf^2 - Xi^2), (it...
28. ### Balancing 3 Forces

Thanks a lot, I hope you will see the diagram ASAP because the project I have due is on Thursday. The equations I set up, are reasonable but there's a "?" that I don't understand. THanx
29. ### Balancing 3 Forces

Hello Everyone, I solved an exercise that has to do with equilibrium. There are 3 forces and I should find the tensions Ta and Tb in the 2 cords. (I drew a simple picture so that it would be more clear to you). I solved the exercise following physical principles (I think I did it correct)...
30. ### Vector Exercises

:rofl: Thank God I have the right concepts on my mind. The problem Jcsd is that I have to submit the answer online and it is not the same as submitting the answer as 53 deg. and 143 deg. This is my dilemma. Anyway I will chose the one with respect to the West East line because it says...
31. ### Vector Exercises

Thanks a lot Jcdsd, I still have a question which I couldn't understand from the book and the professor. Why should we take the angle of the displacement from the East West direction and not from the North line. So I found that the angle is about 53 degrees with the North, but taking it with...
32. ### Vector Exercises

Hello Everyone, In school I had a test of Vector exercises. The problem is that I have to submit them online and I need the exact value for the questions. Anyway I don't want you to solve them for me. I just need some help where I am stuck. The first exercise: A boy runs 3.3 m North, 7.1 m...
33. ### Trig and Vector Components

:uhh: Anyone can give the answer to my questions?
34. ### Trig and Vector Components

:smile: Thank You Tide, What I think now, is forming two simultaneous equations. 1) 17a-99b= -4.3 2) 28b-99a= -78 Solving them, I think is the answer for a and b. Since the i units can't be added to the j units I formed two equations just neglecting i and j. So for i group it will give...
35. ### Trig and Vector Components

Vectors Hello Everyone, In school I had a test of Vector exercises. The problem is that I have to submit them online and I need the exact value for the questions. Anyway I don't want you to solve them for me. I just need some help where I am stuck. The first exercise: A boy runs 3.3 m...
36. ### Help with a derivative

Thanks Gaz! The solution is correct. I had the answer but I couldn't get to it. It's exactly as u have solved it.
37. ### Help with a derivative

The problem is that I can't cancel X from the equation. So it will be INT X*SQR(U) du...?
38. ### Help with a derivative

Hello Everyone, I'm studying the substitution rule for solving integrals. There is an exercise that I can't solve. I know that you will help me. INT X*SQR(X-1) Limit 1->2. I tried all the substitutions but I can't get to the solution. Thanx
39. ### Help with a derivative

Thanks a lot! I just solved the problem.
40. ### Help with a derivative

Optimization "A conical cup is made from a circular piece of paper of radius R by cutting out a sector and joining its edges. Find the maximum capacity of such cup" I just know that V(cone)=1/3 Pi R^2 H and that the lateral Area is A= Pi R Sqr(R^2+H^2) I can't go any further. Thanks...
41. ### Help with a derivative

:approve: I am sorry for inconvenience. I forgot that ln(x+5) - ln(x) = ln (x+5)/x. The exercise was really easy.
42. ### Help with a derivative

L'Hospital Rule Using L'Hospital's Rule I should find the limit of the function Lim x->inf. x[ln(x+5) -ln x] . First it should be differentiated. I wrote the function like this : Lim x->inf. x ln(x+5) - x ln x or Lim x->inf. [ln(x+5)]/(1/x) - ln x/(1/x). I differentiated the...
43. ### Can anybody differentiate this to simplest formy=4/3+5cosx

Hello, I have a limit to solve which in fact involves differentation (L'Hospital's rule) Lim as x->inf. (xe^[1/x]-x) I solved it but I am not quite sure. It can't be solved immediately by substitution because it becomes an undet. form. So applying the Hospital Rule I found Lim as x->inf...
44. ### Help with a derivative

Fortunately I was right, anyway thanks for your help. I found the derivative exactly as you did. Now I should find the maximum. So i should find f(x)' = 0 and f(x)" if it is <0 (max) or > 0 (min). The problem I have now is that I can't find a value for f(x)' (a value for t) so that it is...
45. ### Help with a derivative

Hello everyone, I'm having some difficulties with a problem. It includes an equation and says find the time when it is a maximum. The equation is f(x)=75/(1+74e^(-0.6t)) To find the maximum we'll have to set the derivative of f(x)=0, but the problem I have is differentiating this...
46. ### Copper calorimeter help

Right Doc. :smile: I found first the mass of the steam condensed and it was 49 g. After this I began setting the equalities and as a mass of steam I used 49 g instead of 100. The result was exactly 100Celcius (final temp). Thank you for your help.
47. ### Copper calorimeter help

Thank You for your answer Doc. Fortunately I have only the answers of this exercise (final temp.= 100 d. Celcius and 49 g of steam condensed). The way I solved the exercise is the same as you did. I find the energy given when steam condenses + the energy when this water cools and equal that...
48. ### Copper calorimeter help

Hello, Cruising the internet, I saw this wonderful website. I am a high school senior (in fall college freshman). As I have a lot free time now in summer, I preparing for college. The problem I have has to do with temp. exchange but still I can't solve it right. It says: Determine the...