In FPS system, you need to remember the relations exactly as they are, that is why, you need use conversion factor method.

In SI Units, you need to understand the relations between prefixes. The prefixes are so important and very well related to the decimal points. In SI Units, you just have to know the relative position of the decimal points between the two units, e.g. x.x micrometers, and kilometers. So, the prefix “micro” means it is about 6 decimal places left and right with respect to the x.x meters, and similarly, the prefix “kilo” means, it is about 3 decimal places left or right from x.x meters depending on you want to change kilometer to meter or meter to kilometer. So, you need to draw line diagram first, then decide to move the decimal point left or right depending on their relative position in the line diagram. For Example,

The line diagram can be like as follows:

.km | .hm | .dam | .m | .dm | .cm | .mm | .no name (x 10 mm) | .no name (x100 mm) | .micro meters

So, if you want to convert 10.234 km to millimeters, then you should find their relative position. Millimeter is 6 digits on right side of km, therefore, you need to move six digits to the right as follows:

10.234 km —> 10.234000 km (attach 000 as a placement zero) —> 10234000. mm

Should you convert 1023.40 cm to km, then you need to find the relative position of km and cm, i.e. five digits. km is 5 digits away from cm and it is on left side of cm, therefore, you should move 5 digits to the left as follows:

1023.40 cm —> attach enough zero on the left end of the number, e.g. 0001023.40 cm.
Then, move the decimal point by 5 digits on the left from original position, as follows:

00.0102340 km. The extra zeros on the left may be discarded as long as they don’t carry any meaning, e.g. in this example: 0.0102340 km.

In FPS, e.g.
1 foot = 12 inches. Conversion factors are: 1 foot / 12 inches, or 12 inches / 1 foot. The conversion factor is nothing

Q. 1. In a test drive at VRI, a high powered car goes from 0.0km/hr to 216.0 km/hr in 10.0 seconds?

(a) What is the initial speed of the Car during the test drive? ______m/s

Sol: Initial speed is the speed at the start of the event. If an event is divided into several time segments (or incremental time steps), then the speed at the beginning of each segment (time segment) is considered as the initial speed. In this case we have only one time segment, therefore, there is only one initial speed, i.e. 0.0 m/s

(b) What is the final speed of the Car during the drive? ________ m/s

Sol: Final speed is the speed at the end of the event. If an event is divided into several time segments (or incremental time steps), then the speed at the end of each segment (time segment) is considered as the final speed. In this case we have only one time segment, therefore, there is only one final speed, i.e. 216.0 km/h (Convert the non-zero speeds from km/h to m/s as follows 216 km/h x (1000m/1km) x (1h/3600seconds) = 60.0 m/s)

(c) What is the average speed of the Car during the test drive? ____________m/s

Sol: Average speed is the airthmatic mean of the initial and final speeds.
Mathmatically,
average speed = half of (initial speed + final speed)
OR, average speed = (final speed + initial speed) / 2 = (V_f + V_i) /2

In this numerical example,
average speed = (V_f + V_i) /2 = (60.0 + 0.0 ) / 2 = 30.0 meters/seconds = 30.0 m/s

(d) Compute the distance covered by the Car during the test drive? _____________Meter

(e) What is the acceleration of the Car during the test drive? ____________m/s

(f) Assuming the mass of the car is equal to 1000 kg, compute the net external force applied on car to accelerate the car from 0 m/s to 60 m/s in just 5 seconds. ____________N (=kg x m/s²
]]> http://www.akib.com/?feed=rss2&p=11 0 http://www.akib.com/?p=9 http://www.akib.com/?p=9#comments Wed, 02 Jun 2010 21:12:44 +0000 admin http://www.msui.com/?p=9 Week One: Post # 01: Must do at least one thing.
“A Mandatory Work” on the very first week for BB based course(s)

Hello! Welcome to PHYS 101 BB Course. Thank you very much for your enrollment into this course, named: PHYS 101.

Your postings and participations in this course is very important from the very first day to the end of the course.

Please read the bottom part of this posting. You are required to do at least one of the things mentioned on the list.

By the time you read this posting, a few students might have already posted their very first posting: introducing themselves. If you have not yet done so, then please post it ASAP. Please note that you are required to do one of the following actions to be considered as a participating student. If you don’t do so by 00 HOURS of next Monday, then the university requires me to ban you from accessing this course in immediate effect. That is the rule.

A copy of an email from an admin who monitors the online courses. Please note that the guidelines for the online faculty (attached) have been revised. Every student must do at least one of the following to be considered as him/herself as a participating student:

-post on course discussion boards

-send an email to the instructor within the Blackboard course

-take a test or quiz (this does not include the course tutorial quizzes)

-submit a homework assignment

Thank you,
Instructor PHYS 101

ANS: The speed and velocity problems may be given in km/h or mile/hour, and you will need to convert it first to m/s [i.e. meter/seconds].

Here is an example of unit conversion for your review:

54 km / h ==> 54 km/h x (1000 m / (1km)) x 3600 s/1hr

cancel the common units in numerator and denominator: km in numerator cancels km in denominator, and similarly the hour in numerator cancels hour in denominator. Such that you will
eventually get the final numbers in meter/seconds (i.e. m/s) as follows:

54×1000/3600 m/s = 15 m/s

In PHYSICS, whenever you get QUANTITIES in UNITS other than kilogram (kg), meter (m), and seconds (s), then PLEASE convert each of them to kg, m, and s or their combinations. Most of the units of measurements are in SI units, e.g. Force in SI unit is Newton (N), which is equal to = kg.m/s².

FAQ: What is the most possible mistake we students make in exams?

ANS: Majority of students make mistake in exam not because they don’t know how to solve the numerical problem, but because they simply don’t read it carefully. In numerical problems each word can be misread or skipped when the time is limited, and you have to solve so many questions in a short period of time. Therefore, read, read, and read until you understand the question. Identify the keywords that might change your answer to the other side, e.g. at least, at most, average speed, instantaneous speed, ….. That is why, you should first prepare a list of the variable names, and corresponding values assigned to each variables or constants. Identify the variable that is asked to find, e.g. acceleration, a = ? Based on what is asked and what is given, list the necessary equations to get the final answer. If anything is missing or tricky (not mentioned directly), e.g. speed of a car at rest (usually, such wordings should be converted to numbers), or final speed is doubled, then identify them in mathematical form using equations, again. Once all the given and necessary quantities are identified, then plug these values into equation, and solve for unknowns. One at a time. Usually, students in beginner level Physics are required to solve one equation for one variables, and but in higher level Physics courses, you might need to solve simultaneous equations for more one variable.

FAQ: May we post some numerical problems and you help us solve these problems at your website?

ANS: You are not allowed to post any problem from your homework assignments, or take home exam papers, or assessments (test, quiz, or any form of exam where your work is graded), no matter which college, university, or school or training center you go. Any problem other than the problem in such homeworks and exams to be graded, you may openly discuss in the discussion forum. Your main objective of publishing these problems here should be only to learn and improve your competency on the subject. Anyone who publishes any problem here automatically agrees on these simple rules and will not disobey such rules and pledge, and if required the administrator of this website may disclose the identity of the person to respective authorities, and teachers because such works are considered as plagiarism. Please note that your login name (plus other information as well), and IP address of the computer you used may be passed to the respective school, college, teacher, and/ or the relevant authority. We have zero tolerance on plagiarism. We do not want to be part of plagiarism. Therefore, any problem you solve here on this website will remain as public and available to any body who has access to internet, and may be found via Google Search or other search engines, therefore, you may be caught if you try to plagiarise the works that you were supposed to do by yourself without the help of a third person. You are most welcome to discuss all other numerical problems from top to bottom.

FAQ on Calculator. What type of calculator do you recommend for beginners level Physics course (e.g. PHYSICS 101) ?
ANS : I would prefer to have a simple sicentific calculator as compared to a complex programmable calculator. We will not need an advanced skill on using calculator for an intermediate algebra based computations. If you can handle exponents on your calculator, then you can solve most of the numerical problems. Walmart / Staples / OfficeMax like stores also offer such simple scientific calculators that cost less than $10.

FAQ on Number of Credits. How many credit hours do you suggest when I am taking the beginners’ physics course, e.g. PHYSICS 101 ?
ANS : The maximum number of credit hours that you may take in a given semester will depend on the total duration of your semester. In regular / traditional in-seat fall and spring semester where you spend about 16 weeks in classroom, you should not exceed the credit hours more than 15 for better performance unless you are geek / nerd / ghissu. If you are an average student, 15 credit hours in 16 weeks is just a safe range that you can handle without compromising the grade. If you work 40 hours per week in addition to taking courses in school e.g. evening hours, then you should decrease to minimum e.g. around 6 credit hours. Note that if you take 6 credit hours of regular class, then you need 12 hours of study at home as a match up for average performance in the class as well. Similarly, if you intend to study in online / distance learning, then how long is your semester? If it is 8 weeks, then, you should not take more than 9 credit hours if you are a full time student, and if you work 40 hours per week, then you should not take more than 3 credit hours because it is like taking 6 credit hours in 16 weeks long semesters. The pace of work load move very fast in 8 weeks long semesters, and you need REACTION time to understand the subject matter, therefore, if you take more than 3 credit hours in 8 weeks long semesters and work 40 hours or more, then your brain does not get enough rest time, and also does not have enough REACTION time to think and analyze what you have learnt. If you take more than 6 credits and work more than 20 hours, then your performance will be questionable. You will just look for excuses to put whole blame on third party where your decision of taking too many credit hours was the sole reason for your failure. Well, if you are an extraordinary person, then these rules don’t apply, and you may just neglect them.

Summary: In eight-weeks-long semester, you must focus on study. If you have a full time employment, then the 6 credits coursework will be a too high load. Please note that you need to study (every week) about 50 pages of your Physics textbook (most of the physics textbooks for GenEd students have about 500 pages in about 10 chapters: 1. Motion, 2. Energy, 3. Pressure, 4. Heat/Temperature, 5. Wave, 6. Light, 7. Magnetism, 8. Electricity, 9. Atomic Physics, 10. Nuclear Physics), and do some homework assignments. That is a tremendous study load in one week. You teacher may not reduce the course content just because this is an eight weeks semester. It was designed for those who want to challenge such a comprehensive course in such a short period of time. Your accredation board does not want to listen such excuses. The answer is simple, if you can not handle it, don’t take, but your teacher must meet the basic standard as required by accredation board. Should there be no accredation board, then you might get a letter grade without any study, and it could be possible just by paying the tuition fees as if you are buying a letter grade in your local grocery store.

FAQ: Calculator: What is your suggestions on calculators?

ANS: There are at least five different catgories of calculators available in the current market.

(a) Accountant’s simple calculator: These are for simple addition, subtraction, multiplication, and divisions. No students of Math courses or Physics courses should every waste his/her money on this type of calculator.

(b) Scientific Calculator of lower class: It does not have all the functions that a regular scientific calculator should have. I don’t know why are these calculator manufacturers produce this half baked calculator? Usually this variety does not have permutations (nPr) , and combinations (nCr) functions. If a scientific calculator does not have basic trinometric functions, and basic statistical functions, then don’t waste your money on this type. Therefore, becareful when you want to buy a calculator of this category.

(c) Fully functional scientific calculator: You should have this type of calculator. It usually has all trignometric functions, exponents, logarithmic, and statistical functions. They look a bit complex, but you should have this. You should not compromise on the scientific calculator. Don’t buy the scientific calculator available in Dollar shops, they are very prone to skip keys (either because the keys are too soft or too hard: you get what you pay). You should not regret if your calculator skips a right keys in the exam, and you find your answer messed up because of calculator. This is what I had seen. I will go for two lines or three line model, with inputs editable.

(d) Texas Instruments – economy type. Any calculator that costs more than US $20. is not in my list. Why would you buy a calculator that is heavy, and not useful most of the time.

(e) Texas Instruments – costlier type. Usually high school students have this model, partly because they feel it “cool” (or “hot”) such that they can feel pride on owning such calculator. These calculators are not only very costly, but also heavy to carry in your pocket. Why would want to buy a calculator, that you can never waste your effort to learn its use for solving a few problems.

Some important notes before we start learning basics components of a motion of an object in 1-D context.

Students do regularly complain that they dislike (even hate) learning physics not because it is not interesting, but because it involves complicated mathematical computations. They complain that the content moves so fast that the students need to learn so many things in a short period of time, say in just one semester. The following observations may help you succeed in this course:

1. GenEd Physics course requires you to have prior knowledge on basic and intermediate algebra:

(a) ability of solve linear equation, e.g. Y = A X + B. You should be able to solve one of the two parameters in the equation: Y, X, A, or B. Three of the four quantities in this equation must be given to you, and your job will be to identify and solve the unknown quantitiy: it should be only one in this equation. If you are given only two quantities out of the four, then either the information is incomplete by mistake (or an error) or it is a tricky wording that the value of the third parameter is hidden, e.g. zero.

(b) ability of solve second degree polynomial, usually, a quadratic equation of the form: Y = A X ² + B X + C. You are asked to solve and get the value of X when you are given Y, A, B, C. Easiest way to solve this equation (get the value of X) is to convert this equation to A X ² + B X + C’ = 0 where C’ = C – Y when Y is not zero. Then, use the standard solutions using, X = ( – b + √ (B ² – 4 A C))/(2A) and X = ( – b – √ (B ² – 4 A C))/(2A) .

Once you get these solutions, you must be careful whether both solutions are acceptable or not, if not then you should be able to identify which one is a right solution, and if the other one is not realistic solution from real world perspective. For example, if you throw a ball to sky, and compute how many seconds later it will return to your hand, then you can get two values of durations, one positive, and one negative. Negative is not a realistic solution, and you need to reject unrealistic solutions, but you must mention the reason.

I am adding this virtual lab as one of the important learning resouce tools. If you would conduct some of the virtual labs available on this website, then I firmly believe that your understanding on the subject should improve.

If you are beginner in Physics course, then please don’t focus too much on Mathematical part of the lab work (as it might involve higher level maths), but you should focus on the events: action and results. You should connect these events to your textbook. It is the best and complete virtual physics lab (VPL) among those VPL that I came across in my quest in last couple of years. Take your time.

You may not smell of buring your equipment because you made a mistake or hear the instruments dropped from the table on the floor, but it gives really a great feeling on the experiments for no extra charge. You can do it while seating on your bed room.

Therefore, I suggest you try again and again until you master it. Please note that the real experiments in your real lab are not that precise and correct as you might get in these virtual labs. It is going to be a big deal and therefore, you should not expect same degree of accuracy if you ever try to do similar experiments in real world situations. If possible set your precision and tolerance level to little higher than the default values are set, so that you can easily understand the statistical method we use to get better approximate the measured values close enough to the values obtained from mathematical models.

If a car initially moving with the speed of 108 km/h comes to complete rest in 5 second duration, what is the acceleration?

Convert 108 km/h to m/s as follows:

v= 108 km/h x (1000 m/1km) x (1h / 3600 s) = 30 m/s

Acceleration = Change in velocity / duration = (0-30) /5 = -6 m/s².

Some students might simply use the given information without making necessary conversions, and get the acceleration as follows:

a = (0-108)/5 = 21.6 m/ s². It is obviously wrong. Well, if you use a different unit of measurement then mathematically it is correct, no one else will understand it in first glance unless they spend extra time to figure it out. Therefore, note down the correct unit of measurement at the end of acceleration, a = (0-108)/5 = 21.6 km/hr/s. As a beginner of Physics, I doubt whether it makes any sense to you. Therefore, convert every unit that is not in meter, kilogram, seconds, and/or combinations of these three, then you will never ever suffer. This should be your first step towards learning Physics and making sense out of complex physics problems. If you get lost in the unit of measurements, then I have no hesitation that you will not only lose your precious time, but also get nothing-so-worth knowledge out of this course.

Lets see additional but important SI units of measurements that are in fact combination of kilogram, meter, and seconds.

Force is in Newton which is equal to kg x m / s²

Work (Energy is capacity to do work, thus mathematically, Energy = Work) is in Joule which is equal to Newton x meter = (kg x m / s²) x m

Similarly, Power is Work (Energy is capacity to do work, thus mathematically, Energy = Work) per unit time, thus it is in Watt which is equal to Joule/seconds. It is also equal to Newton x meter/seconds = (kg x m / s²) x m/s. Sometime, Power = Force x velocity [in terms of units of measurements]. If you are a student of higher level physics, then don’t look at the “X” multiplication marks as cross-products. Here, my target student is beginner in Physics, therefore, “.” dot and “X” cross products are not so important to discuss. They don’t need it.

In the next posting, I will discuss on the number digits that you need to consider whenever you need to extract from your 8 or 10 or 12 digits calculator. You are not going to write all the digits of your calculate on your paper. You might lose score if you are not using certain rules in this regard. Please read the next posting to understand how many digits that you can extract from your calculator and present it to the instructor or your boss.

Should you have any questions, please post your questions.

Thank you.
MSUi.com Team
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