Math Is Fun Forum

debjit625

Member

Registered: 2012-07-23

Posts: 101

Physic math problem

Hi,
In a physic book I found this

Is the math correct ? as far my math goes it should be 1.02

Thanks

Last edited by debjit625 (2013-06-11 04:04:01)

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Debjit Roy
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The essence of mathematics lies in its freedom - Georg Cantor

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: Physic math problem

Well, physics books tend to round their answers very much. I think it is acceptable to do so.

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“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

debjit625

Member

Registered: 2012-07-23

Posts: 101

Re: Physic math problem

Well,I thought that but in that case physics books use

approx symbol in general.

So I am right with the math ?

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Debjit Roy
___________________________________________________
The essence of mathematics lies in its freedom - Georg Cantor

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: Physic math problem

Well, you rounded the answer too, but it is correct. That expression is approximately 1.02.

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“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

Re: Physic math problem

hi debjit625

What was the topic?  That will help in deciding what rounding is acceptable.  The cosmological constant for example

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

debjit625

Member

Registered: 2012-07-23

Posts: 101

Re: Physic math problem

Yes stefy I agree with you,  but still we use approx symbol for that... don't we ?,in the book they directly used equal symbol.

Bob the topic was about... calculating vectors...
Their are two force vectors given,first one 70N north and another is 50N south west,so calculate the resulting force and direction.

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Debjit Roy
___________________________________________________
The essence of mathematics lies in its freedom - Georg Cantor

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

Re: Physic math problem

hi debjit625

Ok, thanks.  So they're saying 45.58... is approximately 45 degrees.  If they're going to choose to give the answer to the nearest degree then it should be 46. 

But the important thing is you know what you're doing even if they don't. 

General point about rounding: Do the calculation with as much accuracy as you can throughout.  Then think what is  a reasonable amount of rounding and do it at the end., not during the calculation.

example of what can go wrong.

15 * √24

√24 = 4.898...  round off too soon ---> 5

15 * 5 = 75

Correct value is 73.4846922834953..... so if you round that off to the nearest integer you get 73.

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob