NOOB Questions Answered By Dopamine David

[st3v13]

I dare you to answer this one, David.

The drawing shows a collision between two pucks on an air-hockey table. Puck A has a mass of 0.022 kg and is moving along the x axis with a velocity of +5.5 m/s. It makes a collision with puck B, which has a mass of 0.052 kg and is initially at rest. The collision is not head-on. After the collision, the two pucks fly apart with the angles shown in the drawing.



(a) Find the final speed of puck A. _____ m/s

(b) Find the final speed of puck B. _____ m/s

I don't think this problem is possible for 2 reasons:
1- If 2 pucks hit each other horizontally there shouldn't be vertical force.(tecnicly you didn't state that they hit each other vertically so i'm going to assume that the force they go in the vertical direction will just be equal to each other which i say again in like 3 lines)
2- There isn't enough information.
But I assumed:
The problem is perfectly elastic.
The pucks are going vertically with equal force for lots of reasons i can't remember
Sol:
pucks vertical momentum must be equal
sin(65*)x.022*Va=sin(37*)(.052)Vb
Va= (sin(37*)(.052))/(sin(65*)*.022)xVb
Given the velocity and mass. We can determine the sum of the momentums must, which must be equal in a perfectly elastic solution
Ma x Voa +Mb x Vob = Ma x Vfa + Mb x Vfb
Now substitute the variables
5.5x(.022)+.052x0=.022x((sin(37*)x.052)/(sin(65*)x.022))xVb + .052xVb
Vb = 5.5x(.022)/(.022x((sin(37*)x.052)/(sin(65*)x.022)) + .052)

Vb = 1.3629728~1.363 m/s
Va = 2.2784279~2.278 m/s
Wow i'm a nerd.
~st3v13

(note: I believe david telepathically sent me that answer)

[brainfartalerts]

Oy David,
I suspect I was poisoned by the finger food - either the food itself or someone coughing on it - at an art gallery opening last night and awoke with nausea, chills, sinus headache and general hatred of the world and all its inhabitants so my (lamewhoringpseudolongboarding) question is:

Is there any interest in a custom machined center-set 56mm diameter wheel with a 50mm contact patch and 75A / 78A / 81A / 88A / 92A / 94A / 96A / 98A duro's that starts with a light chamfer on the outer edge to prevent chunking as the outer edge transitions to a smooth wear radius shown in the crappy phone pic?

[Charles]

how do you measure your trucks, i measured mine from the end of one axel to the other and got 210mm, but my trucks definently do not look that big.

Thanks

[lachance333]

im making my first board with baltic birch wich is also known as russian birch but should i be getting 2 1/4 inches and then glue them together or get 1 1/2 inch because on thoothless longboards it tells me method one and one other thing when im going to grip my board should i grip it first and then put the holes for the trucks and stuff and if i put the grip tape first how do i make the holes after////? i know its alot but can someone help me thx alot

[lachance333]

how big is the base of the randall r2 180mm???
i cant help it if im a noob my bad lol

[Ogre]

I don't think this problem is possible for 2 reasons:
1- If 2 pucks hit each other horizontally there shouldn't be vertical force.(tecnicly you didn't state that they hit each other vertically so i'm going to assume that the force they go in the vertical direction will just be equal to each other which i say again in like 3 lines)
2- There isn't enough information.
But I assumed:
The problem is perfectly elastic.
The pucks are going vertically with equal force for lots of reasons i can't remember
Sol:
pucks vertical momentum must be equal
sin(65*)x.022*Va=sin(37*)(.052)Vb
Va= (sin(37*)(.052))/(sin(65*)*.022)xVb
Given the velocity and mass. We can determine the sum of the momentums must, which must be equal in a perfectly elastic solution
Ma x Voa +Mb x Vob = Ma x Vfa + Mb x Vfb
Now substitute the variables
5.5x(.022)+.052x0=.022x((sin(37*)x.052)/(sin(65*)x.022))xVb + .052xVb
Vb = 5.5x(.022)/(.022x((sin(37*)x.052)/(sin(65*)x.022)) + .052)

Vb = 1.3629728~1.363 m/s
Va = 2.2784279~2.278 m/s
Wow i'm a nerd.
~st3v13

(note: I believe david telepathically sent me that answer)

simple.. the "final" speed will be 0.0 m/s

[mc99david]

a lot of good questions.. i cant answer them right now cause im skating, but i will answer them soon

[shortyman801]

Can you take grip tape off of a board without hurting the deck?

Then

can I stain the top of the board, lay down a coat of glass, then throw on some clear tape?

Also


What can I do with an extra pair of bushings I have to make them feel softer; or just something fun I could do with them to kill some time.

[st3v13]

simple.. the "final" speed will be 0.0 m/s

Actually that'd be wrong. Because for this question to be solvable you'd have to assume that it is a frictionless surface.

O another assumption that i forgot... actually you could assume that from the collision being perfectly ellastic.
~st3v13

[brainfartalerts]

Actually that'd be wrong. Because for this question to be solvable you'd have to assume that it is a frictionless surface.

O another assumption that i forgot... actually you could assume that from the collision being perfectly ellastic.
~st3v13

I think Dave means final when the puck falls into the slot at which point the puck will be at rest or briefly delayed from being at rest by the trip from the slot into the losers hand then through the air to it's final resting place embedded in the eye of the winner.

[st3v13]

I think Dave means final when the puck falls into the slot at which point the puck will be at rest or briefly delayed from being at rest by the trip from the slot into the losers hand then through the air to it's final resting place embedded in the eye of the winner.

that's making the assumption that this is a game of hockey w/ 2 pucks. which would totally not make sense and not be essential to solving the problem at hand.
ANYWAYS!! not the point.
ASSUMING THAT THE PROBLEM IS STATED IN THE FOLLOWING CONDITIONS, ITS TRUE:
1- perfectly ellastic
2- frictionless environment
3- it is a physics problem, most likely from your physics class

Now to ask a question: WHat are the degrees of the following trucks:
Tracker RT-X
Tracker Rt-S
Bennet Vector

off for my own challenge... trying to ride a legendary gnome...
~st3v13

[Tonyz]

Why does it hurt when I pee?

Me too, it's dehydration. Drink lots of water, it stops.

[Tonyz]

The bushings will be going on a Superglider with Ace55 trucks (complete I ordered from MHS) I only do cruising/carving for the time being because I live in Arizona...nothin' but flatland out here.

I'm from AZ too, there's some pretty good downhill at South Mountain and Fountain Hills.

[boarders mom]

David I have three questions, and forgive me if they have already been answered on fish.

1) Can you give me a description of the different tuck styles and the pros and cons of each? Pics would be helpful too if possible.

2) I bought the daughter (8 this new years) a diy deck from Subsonic Scott. I knew it was a slalom deck when we bought it but I figured the price was right and it would just get her started. Well now that its all set up it's too high for her to comfortably foot brake. We've tweaked it as much as we can, and a couple people have suggested converting it to a drop through. Scott doesn't think that will work, he's concerned about wheel bite, which we've already had with some of the setups we tried. I'm really hesitant to go cutting this board up in case later she does want a slalom board, on the other hand, the price was right for experimenting. What should I do about the situation now? Give in and buy yet another deck?

3) Any suggestions on how to get my son to improve his grades, so that I can continue to take him to longboard events with a clear conscience? Currently 3 F's and a D, all because he won't do the work.
Thanks for any help David!

[Ogre]

Actually that'd be wrong. Because for this question to be solvable you'd have to assume that it is a frictionless surface.

O another assumption that i forgot... actually you could assume that from the collision being perfectly ellastic.
~st3v13

Wrong again..in order for the collision to be perfectly "ellastic" there would need to be such a word and property. Brian is on the right track...put more quarters up.

Ooops sorry David, I was responding, not answering.

[Foxen]

Bump, as a preventative measure.

[mc99david]

Brainfarts - I do think there is a market for those wheels.. that would be a great mini wheel.

Charles - you measure the trucks from the inside to the inside. So at the part of the hanger where the bearing hits.. the grinding area if you are into that sort of thing. but yeah, 180mm trucks are about 205 if you measure all the way to the outermost part.

Lachance: The base plates are about 2 inches by 4 inches. but not totaly posative. and it doesnt matter, cause you wont drill your holes untill you ahve base plates to use to measure.. or buy one of brainfartalerts sticker templates, They are a life saver imo. Also, drill your holes, then grip.

Shortyman: you can take grip off.. but its a pain. you can use a hair dryer to heat up the glue and then pull it off, there will still be glue remaining.. taking this off is a pain, even with proper solvents, but you can use things like mineral spirits to work on this, and staining and re taping will definitly all work just fine... but its not fun, and its a pain, just a heads up

and sometimes you can make bushings feel softer by soaking them in lighter fluid.. but this will also cause them to break down.. I say spend $3 and buy softer bushings.

Steve: Those are slalom style trucks.. I wont answer the question mostly cause I dont know degrees of standard geomitry trucks at all..

Boardersmom: Brazilian, knee on the board.. this is super stable, great for turning, and you can hold it all day long, but the aerodynamics of it are not the best.

American - strait legs, bend at the waist. can be very good, but it does make you very tall and easy to draft

Euro - pretty much what everyone doesn, stand up, but rest your chest on your quad. you are lower, not as much movement if you need to grab a rail or put a hand on the ground.

The fastest guys seem to do a euro, or a euro that is a little bit taller and nearly american.

2. I would get her a new board. cuting into one to make it Drop through is enough work to build a new one from scratch imo, and that will make it so that it is made ot be a drop through. that being said, she can get used to a tall board just fine.. My oldest at 4 yo rides a top mount. and once she gets foot breaking like that, she will be very good at it. I am a believer in not making the board easier for you to do something, but getting better at something because the board creates more of a chalenge.

3. I was the same way as your son when i was in school. I have always had a great work ethic, but when it came to school i just always did terrable, and didnt do my homework ever, and always failed tests. No amount of punishment helped this. My issue was that I did not see any real life reason as to why i need to do any of that. And its true. Since highschool, i have not spoken a word of french, have needed basic math skills, and have needed basic writting skills. None of the books i read in english have made any sort of difference at all. Really, the stuff that I need to know now, and the stuff I remember could be taught in 6 months. and that makes up for all of jr high and highschool.

Now what i have said is not helpful, i understand that what he needs is application imo. He needs to know why its important to know this stuff. I learned and paid attention to the things that I knew would help me later on. American history, with the constitution, the legal proces, the governement structure, Math with Geometry and Algebra, helped me build skateboard ramps, and are just great throught processes for how your brain should annalyze things to begin with. There are more than that. but with my kids i plan to start working towards what carreers they are wanting to do, or what carreers could peak there interest, and show how things that they are being taught could make them successfull later on.

if he thinks like me, then this is what he needs, cause besides that, there is no point.. and to a degree he is right.


and to everyone else... why are still talking about a math equation that is missing tons of fundamental information to actualy solve?

[K-SHIZZ]

is a foam core/carbon fiber/BB dancer worth it? or would it just be better to go all BB. also what would the pros/cons be of foam/CF

[mc99david]

for a dancer.. I dont think there is any reason to do all that.. Foam and carbon are made to be light, and dampen, and create rigidity in the proper places.. None of these things i think would be good on a dancer.. I really think that Baltic birch is best for them. I love how this stuff flexes, and works in general.. thats my opinion on it. I think foam and carbon are best applicable for dh, and wood and carbon or glass are great for a carver.. but in both cases, i like this stuff best when you want an extremely quick responsive board.

[$tauberC]

I have some bright white gym shorts. I threw a big pendy at the bottom of a run a I dragged my ass on the ground. Now there is road all over them. My mom and I have both tried everything to get it out but nothing has prevailed. I really like these shorts so, can they be saved? How would you clean them?