Recent content by Paulo Serrano

Around the x-axis. answer is pi/8(e^(2pi)-1) It looks kinda similar...but not quite.

Are you sure that's where I made my mistake? The reason it became positive (I think) is not that I got the anti-derivative mixed up. It's because the negative sign outside the parenthesis canceled out the one before the pi*integral of cos2x/2

Hey. Thanks in advanced for the help. This site has helped me a lot through the years. Homework Statement Find the volume of the solid formed by rotating the area within y=e^x and y=sin x when 0<x<pi Homework Equations The Attempt at a Solution I've tried it like 10 times on...

That "actual angle" is the angle from the horizontal line (the water line) and the red line representing the light from the lamp (the one that is smaller than 53 degrees). And yeah, I guess it makes sense than 90-53=37, but why that is the right answer I do not know.

Homework Statement [PLAIN]http://img203.imageshack.us/img203/3072/refractiong.jpg The apparent angle from the water is 53 degrees, but what is the actual angle from the water? Homework Equations n1 * sin i = n2 * sin r The Attempt at a Solution I think the real problem here...

I don't know, but I did the exact same thing as you.

Optics -- How long can I see an objects reflection Homework Statement The object is traveling at a constant velocity of 4 m/s. Initially, the observer can not see the object. At a certain point, the observer can see the reflection of the object in the mirror. For how many seconds is the...

I was able to do it using LCKurtz method, but I wonder if using the circle formula would be faster. Can you help me out a little bit more? Can you give me one of the 3 equations I would make? I just need to know what to do with x_0 and the y_0

Homework Statement The points (-6,2), (3,-1) and (-5,-5) are all points on circumference of the circle. What is the radius of this circle?Homework Equations I don't know what to do. The Attempt at a Solution Have no idea really. I tried actually making a makeshift graphical representation of it...

This was from the test to major in physics/engineering from Rio De Janeiro Federal University last year. The answer sheet says you have to use Fibonacci numbers. I have no idea what those are or how they work, so I'm going to read about them on wikipedia. if someone can give me a summary of how...

Homework Statement A person can go up one step at a time, skip a step at a time, or skip two steps at a time, with the exception of the final step, which obviously you can only go one step up. a) Calculate the different ways someone can up up a staircase with 7 steps. b) Calculate the...

This question is from a national college entrance exam in Brazil. We're not allowed to use calculators, so I rounded g=9.81m/s to 10m/s. Can you enlighten me on that formula you used to find the time? (x=vt) Just a name or wikipedia link will suffice. :) edit: nevermind, I'm an idiot. That's...

Homework Statement An elevator, with people in it, has a mass of 1400 kgs. The motor is hooked up to the power grid that provides 220 volts of power. The elevator has to go up 30 meters at 4m/s. How many watts of potential (not sure if it's called that) are required to get the elevator...

q is heat energy, correct? Why is one the negative of the other?

Homework Statement How many grams of 20 degree C water do I need to add to 100 grams of 80 degree C of water to get the final temperature down to 50 degrees C? Homework Equations I'm sure it's a pretty simple equation, but I don't know it. (I'm studying a lot of different things at once...