|
Author
|
Topic: Using your common sense to solve a physics problem.
|
coffee_addict
Member (Idle past 506 days) Posts: 3645 From: Indianapolis, IN Joined: 03-29-2004
|
|
Message 1 of 188 (143823)
09-22-2004 2:25 AM
|
|
|
I've been thinking about using common sense rather than skills you learn in school to solve real life problems. I'm not going to say who (you know who you are), but someone has been claiming that common sense alone is enough to allow a person to know as much, if not more, than any "jerk scientist". This got me thinking. Can common sense really bring a person that far ahead? Is the person in question's common sense trustworthy? The following is a simple physics problem that was on my entrance exam quite a while ago. What I will post will come in two parts. Part one will only have what they usually give you on a problem. Part two I will give all the equations, constants, and whatnot necessary to solve the problem. You don't need to know anything about physics to be able to complete the problem once you've read part 2. What you will need is a really good common sense. The intention of this is to allow you, or anyone, to test out whether common sense is as great as it seems. If you like a challenge, do not read part two. However, I think it is more fair that part two is included simply because you are not a physicist and I don't expect you to know this off the top of your head. After you've read part 1 and 2, you only need a calculator and common sense to solve the problem. Everything you need is there. By the way, we rarely ever get that much info on our physics problems. Part 1 An automobile driver traveling down an 8% grade slams on his breaks and skids 30 meters before hitting a parked car. A lawyer hires an expert who measures the coefficient of kinetic friction between the road and the tires to be 0.45. Is the lawyer correct to accuse the driver of exceeding the 25 MPH speed limit? Why or why not? (Assume that an 8% grade means that the road raises 8 meters vertically for every 100 meters traveled horizontally. Also, drag is negligible.) Part 2 Uk = coefficient of kinetic friction = 0.45 tan(d) = a/b where d is an angle of a right triangle.
2*a*(x2 - x1) = v2^2 - v1^2 where a = acceleration, v1 = initial velocity, V2= end velocity, x1= initial position, and x2 = end position. F = m*a where F is force, m is mass of the car, and a is acceleration. F(fric) = Uk*m*g*cos(d) where F(fric) is friction force and g is 9.8 m/s*s F(grav) = m*g*sin(d) where F(grav) is the force on the car due to Earth's gravity.
Added by edit: For those that are also frustrated by the term "jerk scientist", please please please do not get involve. Yes, I am sticking my neck out really far by giving handing him/them the answer on a silver platter. Added by a second edit: 1 mile = 1609 meters This message has been edited by Darth Mal, 09-22-2004 03:24 AM
The Laminator
B ULLS HIT For goodness's sake, please vote Democrat this November!
|
coffee_addict
Member (Idle past 506 days) Posts: 3645 From: Indianapolis, IN Joined: 03-29-2004
|
|
|
Message 3 of 188 (143839)
09-22-2004 4:25 AM
|
Reply to: Message 2 by Nighttrain
09-22-2004 3:53 AM
|
|
The offending driver is a fundy. The lawyer is not a fundy, obviously.
The Laminator
B ULLS HIT For goodness's sake, please vote Democrat this November!
| This message is a reply to: | | | Message 2 by Nighttrain, posted 09-22-2004 3:53 AM | | Nighttrain has not replied |
|
coffee_addict
Member (Idle past 506 days) Posts: 3645 From: Indianapolis, IN Joined: 03-29-2004
|
|
|
Message 4 of 188 (143893)
09-22-2004 12:49 PM
|
|
|
Bump
Yup, that sure was a bumpy ride to Pumpkin Fest.
The Laminator
B ULLS HIT For goodness's sake, please vote Democrat this November!
| Replies to this message: | | | Message 5 by Percy, posted 09-22-2004 5:39 PM | | coffee_addict has replied |
|
coffee_addict
Member (Idle past 506 days) Posts: 3645 From: Indianapolis, IN Joined: 03-29-2004
|
|
|
Message 7 of 188 (143945)
09-22-2004 7:06 PM
|
Reply to: Message 5 by Percy
09-22-2004 5:39 PM
|
|
Re: Bump
What Percy said.
The Laminator
B ULLS HIT For goodness's sake, please vote Democrat this November!
| This message is a reply to: | | | Message 5 by Percy, posted 09-22-2004 5:39 PM | | Percy has not replied |
|
coffee_addict
Member (Idle past 506 days) Posts: 3645 From: Indianapolis, IN Joined: 03-29-2004
|
|
|
Message 8 of 188 (143950)
09-22-2004 7:29 PM
|
Reply to: Message 6 by Ooook!
09-22-2004 5:55 PM
|
|
Ooook! writes: Your problem made me think about the nature of science and its relation to common sense. I came to the conclusion that almost every scientific discipline I could think of (apart from the obviously anti-intuitive ones like quantum physics) was the application of common sense once you know the details.
Science is just taking common sense and discipline it to a point where one can relate past events to explore new ones. For example, it's common sense that I can describe how fast I am walking by saying something like "I walked all the way to... wonderland in 10 minutes." Well, if one thinks about it, by purely using common sense, one can apply such a concept to something else more complicated, like how long does a horse take to get to wonderland. If it takes a horse only 1 minute to get to wonderland, one now has the basic concept of relativity, that the horse is relatively faster than me. If wonderland is 1 mile away, one can use his common sense to think, "well, gee, Lam's speed is 1 mile per 10 minutes and the horse's speed is 1 mile per 1 minute. Therefore, the horse is... let me see... that's 1, 2, 3, 4... the horse is 10 times faster than Lam." Just by pure common sense, I've got the basics for the concept of velocity. So yes, I really think that science is just disciplining common sense to a point where one can apply past experiences to predict and explain future events. However, what I don't like is people claiming that undisciplined common sense gives a person the same skills as someone that has been disciplining his common sense for decades. Going back to my problem, everything that you need to solve the problem is there. You don't even need to know much about physics to be able to solve it. All you need to know is that the total force equals the addition of the individual forces involved. For example, say that F(total) is the total force, F(1) and F(2) are 2 individual forces at work, the equation would look something like: F(total) = F(1) + F(2). There, I've given away the answer. This would take me about half a minute to figure out, but I am well trained in this kind of physics. I wouldn't expect an average person to recognize it this fast, although I would expect anyone with a good enough common sense to be able to put together the very obvious puzzle.
The Laminator
B ULLS HIT For goodness's sake, please vote Democrat this November!
| This message is a reply to: | | | Message 6 by Ooook!, posted 09-22-2004 5:55 PM | | Ooook! has replied |
| Replies to this message: | | | Message 9 by Rei, posted 09-22-2004 7:53 PM | | coffee_addict has not replied | | | Message 10 by crashfrog, posted 09-22-2004 8:05 PM | | coffee_addict has replied | | | Message 21 by riVeRraT, posted 09-23-2004 6:14 PM | | coffee_addict has replied | | | Message 62 by Ooook!, posted 09-24-2004 5:39 AM | | coffee_addict has replied |
|
coffee_addict
Member (Idle past 506 days) Posts: 3645 From: Indianapolis, IN Joined: 03-29-2004
|
|
|
Message 11 of 188 (143956)
09-22-2004 8:09 PM
|
Reply to: Message 10 by crashfrog
09-22-2004 8:05 PM
|
|
Look at the picture.
The Laminator
B ULLS HIT For goodness's sake, please vote Democrat this November!
| This message is a reply to: | | | Message 10 by crashfrog, posted 09-22-2004 8:05 PM | | crashfrog has not replied |
| Replies to this message: | | | Message 12 by Nighttrain, posted 09-23-2004 1:19 AM | | coffee_addict has not replied |
|
coffee_addict
Member (Idle past 506 days) Posts: 3645 From: Indianapolis, IN Joined: 03-29-2004
|
|
|
Message 13 of 188 (144000)
09-23-2004 1:31 AM
|
|
|
I'm going to give another big hint tomorrow if noone that's an advocate of the common sense versus "jerk scientist" tries to solve it by then.
The Laminator
B ULLS HIT For goodness's sake, please vote Democrat this November!
|
coffee_addict
Member (Idle past 506 days) Posts: 3645 From: Indianapolis, IN Joined: 03-29-2004
|
|
|
Message 14 of 188 (144168)
09-23-2004 4:53 PM
|
|
|
Ok, here comes another big clue. I stated before that F(total) = F(1) + F(2). Here is the hint. F(1) = F(grav) and F(2) = -F(fric). If you look at the picture again, F(fric)'s arrow is pointing the opposite direction of F(grav). Therefore: F(total) = F(grav) - F(fric) I'm getting a little irritated. What ever happened to common sense?
The Laminator
B ULLS HIT For goodness's sake, please vote Democrat this November!
| Replies to this message: | | | Message 15 by Percy, posted 09-23-2004 5:21 PM | | coffee_addict has replied |
|
coffee_addict
Member (Idle past 506 days) Posts: 3645 From: Indianapolis, IN Joined: 03-29-2004
|
|
|
Message 25 of 188 (144200)
09-23-2004 6:31 PM
|
Reply to: Message 15 by Percy
09-23-2004 5:21 PM
|
|
Percy writes: Except for the tedium of going through the actual steps, your problem is too simple. I'm more interested in the solution to Crash's problem. I can't remember the equations for rotational momentum or energy, I couldn't find them on the web, and now it's bothering me, I want the answer.
That's just it. The frog's problem wasn't really fair, because you can't use common sense for it. You have to have the formula for it to be able to solve it. My problem is designed specifically so that all you need is common sense and a calculator. My original intent is to test out the common sense of those that claim their common sense to be more productive than the years of experience of scientists. Now really, how the hell are we suppose to believe that their common sense is enough to solve such a big puzzle as the age of the earth when they can't even solve something as simple as this? This message has been edited by Lam, 09-23-2004 05:36 PM
The Laminator
B ULLS HIT For goodness's sake, please vote Democrat this November!
| This message is a reply to: | | | Message 15 by Percy, posted 09-23-2004 5:21 PM | | Percy has not replied |
| Replies to this message: | | | Message 32 by crashfrog, posted 09-23-2004 6:53 PM | | coffee_addict has replied |
|
coffee_addict
Member (Idle past 506 days) Posts: 3645 From: Indianapolis, IN Joined: 03-29-2004
|
|
|
Message 26 of 188 (144201)
09-23-2004 6:35 PM
|
Reply to: Message 21 by riVeRraT
09-23-2004 6:14 PM
|
|
the rat writes: My common sense would tell me however that the problem can be solved to a certain degree of accuracy. However it could never be totally accurate, as there aer many variables to consider, besides the ones you mentioned. but it would be close enough to say, yes he was speeding, or no he wasn't. This holds true for many things in science, and sometimes we tend to say yes or no, when we really don't know the answer. If you can understand that, then you will know where I'm coming from.
For a start, could you name some of the variables not already mentioned that would throw off the result? No, you do not need the mass of the car. This is also a really big hint.
The Laminator
B ULLS HIT For goodness's sake, please vote Democrat this November!
| This message is a reply to: | | | Message 21 by riVeRraT, posted 09-23-2004 6:14 PM | | riVeRraT has replied |
| Replies to this message: | | | Message 41 by riVeRraT, posted 09-23-2004 11:40 PM | | coffee_addict has replied |
|
coffee_addict
Member (Idle past 506 days) Posts: 3645 From: Indianapolis, IN Joined: 03-29-2004
|
|
|
Message 27 of 188 (144206)
09-23-2004 6:39 PM
|
Reply to: Message 23 by riVeRraT
09-23-2004 6:22 PM
|
|
the rat writes: Besides all the paper work in the world, and formulas, you might still miss something, that I would see through my common sense, honed by 24years of mechanical hands-on experience. I pity the engineer that doesn't respect that.
I pity the mechanics that don't respect 200 years of scientific inquiries. Edited to change "doesn't" to "don't." I'm a moron and I still don't use singular and plural stuff right by instinct. This message has been edited by Lam, 09-23-2004 05:44 PM
The Laminator
B ULLS HIT For goodness's sake, please vote Democrat this November!
| This message is a reply to: | | | Message 23 by riVeRraT, posted 09-23-2004 6:22 PM | | riVeRraT has replied |
| Replies to this message: | | | Message 42 by riVeRraT, posted 09-23-2004 11:43 PM | | coffee_addict has not replied |
|
coffee_addict
Member (Idle past 506 days) Posts: 3645 From: Indianapolis, IN Joined: 03-29-2004
|
|
|
Message 30 of 188 (144215)
09-23-2004 6:48 PM
|
Reply to: Message 23 by riVeRraT
09-23-2004 6:22 PM
|
|
the rat writes: They hire $30,000 a year engineers...
Hehehe. I just noticed this. All my brothers and sisters are engineers of some sort and none of them started their career with such a low salary. The lowest among them when they started was almost 50,000, and that was over 6 years ago. You're getting some crappy engineers.
The Laminator
B ULLS HIT For goodness's sake, please vote Democrat this November!
| This message is a reply to: | | | Message 23 by riVeRraT, posted 09-23-2004 6:22 PM | | riVeRraT has replied |
| Replies to this message: | | | Message 47 by riVeRraT, posted 09-24-2004 12:16 AM | | coffee_addict has not replied |
|
coffee_addict
Member (Idle past 506 days) Posts: 3645 From: Indianapolis, IN Joined: 03-29-2004
|
|
|
Message 31 of 188 (144217)
09-23-2004 6:50 PM
|
Reply to: Message 29 by Melchior
09-23-2004 6:44 PM
|
|
Melchior writes: I can help you out if you send a PM.
We have PM here? Strange that I've been missing that all along. Where can I go to see mine?
The Laminator
B ULLS HIT For goodness's sake, please vote Democrat this November!
| This message is a reply to: | | | Message 29 by Melchior, posted 09-23-2004 6:44 PM | | Melchior has replied |
| Replies to this message: | | | Message 34 by Melchior, posted 09-23-2004 6:59 PM | | coffee_addict has not replied |
|
coffee_addict
Member (Idle past 506 days) Posts: 3645 From: Indianapolis, IN Joined: 03-29-2004
|
|
|
Message 33 of 188 (144220)
09-23-2004 6:56 PM
|
Reply to: Message 32 by crashfrog
09-23-2004 6:53 PM
|
|
Hahaha. True. I haven't done kinematics for 2 years and am too lazy to look into it now.
The Laminator
B ULLS HIT For goodness's sake, please vote Democrat this November!
| This message is a reply to: | | | Message 32 by crashfrog, posted 09-23-2004 6:53 PM | | crashfrog has not replied |
|
coffee_addict
Member (Idle past 506 days) Posts: 3645 From: Indianapolis, IN Joined: 03-29-2004
|
|
|
Message 45 of 188 (144322)
09-23-2004 11:59 PM
|
Reply to: Message 41 by riVeRraT
09-23-2004 11:40 PM
|
|
the rat writes: would like the mass of the car... Ok, if you must. The mass of the car is 1 gram.
The Laminator
B ULLS HIT For goodness's sake, please vote Democrat this November!
| This message is a reply to: | | | Message 41 by riVeRraT, posted 09-23-2004 11:40 PM | | riVeRraT has replied |
| Replies to this message: | | | Message 53 by riVeRraT, posted 09-24-2004 2:17 AM | | coffee_addict has not replied |
|
™ Version 4.2