Recent content by i_m_mimi

omg that's great i get it now :D When the water is 3 metres deep in the tank, its surface is rising at the instantaneous rate of 2 metres per hour. That means h' = 2, not r' = 2 4/9 pi (3)^2 (2) = 14pi - 3k k = 2pi thanks so much

I get something like if h' = 3 since r' = 2 12/9 pi h + 14pi/h = k Not sure how to isolate for so its 2pi h?

I'm closer to the answer now, but still something wrong P- 1000= Ce^{-kt} I tried using this equation, but my answer was something like t = 10*ln 0.5 / ln(3/5) Tried it again using another equation you gave me: dP/dt = −k(P(t)−A) dP/[P(t)-A] = -kdt took the integral of both...

I made a mistake in copying the question. Water from the hose pours in at a rate of 14pi cubic meters/hour instead of 14, if that makes things simpler. However, I'm still confused. I solved to the point of getting the integral you got following what you did. I got something like 98-14kh +...

I think I've got it :) how did you create those math symbols and format it that way? was it through the physicsforums website coding or by a program? f'(2) = 3 x = 2 lim x->2 [f(x) - f(2)]/(x - 2) * lim x->2 1/ [sqrtx - sqrt2]/(x-2) = (3) * 1/f'(sqrtx) = 3 * 1/(1/2sqrtx) = 3 *...

Homework Statement [10] The air pressure in an automobile's spare tire was initially 3000 millibar. Unfortunately, the tire had a slow leak. After 10 days the pressure in the tire had declined to 2800 millibar. If P(t) is the air pressure in the tire at time t,then P(t) satis es the di...

Homework Statement Suppose that f' (2) = 3. Find the limit as x approaches 2 of [f(x)−f(2)]/[sqrt(x) - sqrt(2)] Answer: 6*sqrt 2 Homework Equations The Attempt at a Solution f'(x) = lim h->0 = [f(a +h) - f(a)]/h = slope [f(x)-f(2)]/ x-2 a = 2 i would think that the limit =...

Homework Statement [10marks] A water tank has the shape of a vertex-down right circular cone. The depth of the tank is 9 meters, and the top of the tank has radius 6 meters. Water flows into the tank from a hose at a constant rate of 14 cubic metres per hour, and leaks out of a hole at...

This is for Math 12, which is the course right before Calculus 12. I factored it like (cosx-2)(cosx+1), but now I realize that would give cos^2(x) - x - 2 = 0, not cos^2(x) - x + 2 = 0 I did plug and chug for the answer from the multiple choice, but I'm curious as to how to get the...

1. Sin^2(x) = 3 – x Answer: 2.97 Attempts: 1-cos^2(x) = 3 – x cos^2(x) - x + 2 = 0 Factored it and got x = pi = 3.14 It’s a multiple choice question, and other answers were 3.02,3.09 which are few decimal places off so the answer must not be pi since it's not even a choice. Is the...

Homework Statement 7. A fireman is standing on top of a building 20.0m high. He finds that if he holds the hose so that water issues from it horizontally at 12.0m/s, the water will hit a burning wall of an adjacent building, at a height of 15.0m above the ground. What is the horizontal distance...

One more question, what is the relationship between the speed and the back emf? I assume directly proportional? How would I be able to calculate the back emf, knowing the frequency?

Oh I get it! So basically, "A current exists in the coil (electrical energy) and it will experience a force in the magnetic field causing it to turn. (mechanical energy)" The counter emf thing is sort of what happens like a side effect. The counter emf would never overwhelm the original emf...

Homework Statement How do motors work? Is what I have right so far? The attempt at a solution Generators: I understand that a coil moves and it cuts across the magnetic flux lines in a magnetic field, emf is induced. So mechanical energy (coil moving) changes into current from the emf...

Unfortunately, I have no idea what it is talking about. Too many big words. I'm only in the 10th grade. I don't really understand it, but I think you're on to something. While incident light is totally reflected the electromagnetic field component penetrates a short (tens of nanometers)...