1 more posts in this thread. [Missing image file: waterfall_of_light_by_lairis77-d38ets9.jpg]
Got a physics I problem I'd like some help with if anyone is up for helping a brother out. Just guidance is more than sufficient. It seems like a basic circular motion problem, but I missed the lecture on it when my professor taught it in class. Here's the problem:
The angular velocity of a process control motor is w = (20 - .5*t^2) rad/s, where t is in seconds.
a. What time does the motor reverse direction?
b. Through what angle does the motor turn between t = 0 s and the instant at which it reverses direction?
So here's my thought process on this one. For part a), set w (the angular velocity) to 0 to solve for t (where I'm guessing is the point that the motor changes direction). So
0 = 20 - .5*t^2 >> t = sqrt(40) s.
For part b), take the derivative of the equation to get the angular acceleration, plug it into
Af = Ao + wi*t + .5(alpha)*t^2 to get the answer in radians, then convert to degrees if I want to. I ended up getting -20.13 degrees for my final answer, or 125.49 rads.
This question doesn't exist on any website (trust me, I've tried looking) so there is no way I can check my answer (not in the back of my textbook). Any guidance AT ALL will be most appreciated!
15 more posts in this thread. [Missing image file: 1358629667202.jpg]
Check the boxes beside the statements that are TRUE, regarding force and motion.
Select all that are True.
1 If an object's speed does not change, no net force is acting on the object.
2 In order to not slow down, an object moving at a constant velocity needs a small net force applied.
3 If two different objects are under the influence of equal forces, they will have equal accelerations.
4 The net force acting on an object that maintains a constant velocity is zero.
5 The net force acting on an object that remains at rest is zero.
6 If a net force acts on an object, the object's velocity will change.
Review Newton's First and Second Laws and the definition of acceleration.
0 more posts in this thread. [Missing image file: oslon_efficiency.png]
Sorry for bothering you, /sci/, but I need to find out how bright an LED is in lumens. For some reason osram decided to list radiant power instead of lm/W for monochrome leds, and I'm struggling with conversion. Wiki lists that ideal monochromatic source at 555nm is 683 lm/W, but this one is dominant 645nm and I have no idea how to obtain a corresponding number. Using 683 lm/W I'd get 327 lm/W for this LED and it's impossible, afaik there is no such efficient LED. That would be nice though.
Here is a data sheet.
51 more posts in this thread. [Missing image file: 1354656462029.jpg]
I was staring at this picture when dad walked past my room, he walked in and asked who these people are.
I pointed to Einstein and Curie and said you should know who these two are, he said yes.
I then pointed to Planck, Bohr, Lorentz, Schrondinger and Heisenberg and asked again, he said he had no idea.
He asked about what they contributed to science, I told him about quantum entanglement (which he had never heard of before), I told him about the constant debates between Einsten and Bohr about determinism and a probabilistic view of the universe, I also told him about quantum superposition.
He asked about what quantum entanglement proves, I told him that it could be used for long distance communication, possibly even teleportation.
He just nodded and said, good. Then walked off.
Did I ruin my chance to explain science to a deepy religious man or was I right when I said entanglement can be used for communication with 0 time delay