Math Is Fun Forum

whoops! Sorry Jane, I forgot about this thread.

The acceleration is in 2 dimensions and therefore has two componants. The book gives the answer as (2.35)i - (1.57)j

You gave the acceleration of the boxes, they want the acceleration of the center of mass.

Anyway, the reason i asked about summing individual forces, is this. Yes, canceling forces are a waste of time, but that still takes care of them. So I can basically just note that cancelling forces can be ignored. However, i believe canceling forces do not necessarily mean the force is internal. Know what I mean?

In otherwords, I'm hoping if i'm unclear about what are internal or external, i can just sum all the individual forces to find Fnet and internal forces will be taken care of. However, I still think i need to be able to identify an internal force.

Right now I'm thinking maybe its two parts of the system acting directly against eachother, rather than a force on one part of the system thats acting on one part, and eventually acting on another part after its been altered.

Right! And all of what you say makes sense! But doesn't this defy the books statement? I mean we are talking about newtons second law for a system of particles, and we are told that the total mass, times the acceleration of the center of mass of the entire system is equal to the sum of the net external forces (with internal forces ignored).  If the force of the rope is internal for the entire rope-block system, then wouldn't that imply, as i explained earlier, that the acceleration of the center of mass is zero in the horizontal direction?

In otherwords, you said the force would be internal for the entire rope block system. Is that not the system we are considering? Isn't newtons second law for a system of particles used when you want to consider the entire system rather than the individual parts?

WHEW! thanks for clearying that up for me, Jane! It was annoying me to no end! Now it makes perfect sense and doesn't annoy me. HUZZAH!  The thrill of comprehension!

the purpose of this puzzle is by no means to save memory or time, its just a puzzle for fun.

However, what I like about TheDude's method is you could use it in assembly to swap the values in two registers without having to use an extra one. Pretty cool!

Does anyone else have any fun code wielding challenges? post them here!

hehehe!

Well here's

Todays subject: internal and external linkage!

I'm just reading about namespaces in my C++ book for the first time. It began by introducing the subject of linkage, but its description is rather unclear.

here's my books description:

okay, but they don't explain what a 'translation unit' is. Immediatley after it uses the following listings to demonstrate internal and external linkage

first.cpp

int externalInt = 5;
const int j = 10;
int main()
{
  return 0;
}

second.cpp

extern int externalInt;
int anExternalInt = 10;
const int j = 10;

after this it says the externalInt variable defined in line 1 of first.cpp has external linkage.

I don't follow. First, this is the first time i have ever seen the 'extern' keyword. So i'm not sure what the first line in second.cpp means, and how many instances of externalInt there are.

Usually my book explains things better than this.  Can anyone explain to me whats happening between these two .cpp files?

Jane, perhaps i didn't make it clear, the idea is that the man is pulling on the rope such that the total tension in the rope is 1000N. So the idea is he IS standing on the beam, but there IS movement. He's pulling his platform upward.

We use WileyPlus. So far its been pretty good. This is the first thing i've found so far.