# Homework Help: Help with simple secondary school Physics question.

1. Jan 13, 2010

### iZH

1. The problem statement, all variables and given/known data
Convert the number below by giving the answer in standard form.

2. Relevant equations
1) 0.0012m(to the power of 2) = _____ cm(to the power of 3)
2) 12kmh(to the power of -1) = _____ ms(to the power of -1)
3) 12ms(to the power of -1) = _____ kmh(to the power of -1)

My effort of showing that i tried.
1)2)3) i convert the number to cm/ms/kmh first. then change it to standard form, but i still dont get what the question really want, and what is the step required. And the answer look really strange. I've been trying this for the whole afternoon untill now.

P/S I saw a lot of complicated question being asked here, but i am new to Physics, and currently stuck at my Physics Chapter 1 homework which is a secondary school standard.
Hope i get a proper formula with answer ASAP. Thanks T_T

Last edited: Jan 13, 2010
2. Jan 13, 2010

### vela

Staff Emeritus
Do you have a typo in the first problem? What do you mean by "standard form"?

3. Jan 13, 2010

### iZH

well, typo for grammar is a yes i guess. But not "standard form" i think.

Kay, i'll give you an easier example that i know.
Convert the number below and write the answer in standard form.
(A) 7.2m to cm
So, it's 720cm after converted. And so, the answer in standard form are,
7.2 x 10(to the power of) -2 cm

Yes, if my post confused you, i'm sorry for the inconvenient caused. Because this is what i learned recently, and i'm new to this forum.

Edited*
Oh yeah, another name for "Standard Form" is called the "Scientific Notation".
-Standard form is based on powers of base number 10. In standard form, the magnitude or numerical value of physical quantity can be written as:

A x 10 (to the power of) x

Last edited: Jan 13, 2010
4. Jan 13, 2010

### vela

Staff Emeritus
OK, that's what I thought you meant by "standard form". The typo I'm referring to are the powers in the first problem. There's no way to convert m2 to cm3.

5. Jan 13, 2010

### iZH

Yes, that's one of the problem that i don't understand too, if you say so, then i guess maybe it's my teacher's mistake for the powers typo.
Thanks for pointing that out.

But do you have any ideas on how to solve the 2nd and 3rd question?

6. Jan 13, 2010

### vela

Staff Emeritus
OK, you have 12 km/h and you want to convert it to m/s. First, note that

$$1~\mbox{km} = 1000~\mbox{m} \rightarrow \frac{1000~\mbox{m}}{1~\mbox{km}} = 1$$

Since multiplying by 1 doesn't change anything, you have

$$12 \frac{\mbox{km}}{\mbox{h}} = 12 \frac{\mbox{km}}{\mbox{h}}\times \frac{1000~\mbox{m}}{1~\mbox{km}}$$

Now the km in the numerator of the first factor cancels with the km in the denominator of the second, leaving you with

$$12 \frac{\mbox{km}}{\mbox{h}} = 12000 \frac{\mbox{m}}{\mbox{h}}$$

You do the same sort of thing to change the h in the bottom to s, using the conversion factors

$$1~\mbox{h} = 60~\mbox{min}$$

$$1~\mbox{min} = 60~\mbox{s}$$

7. Jan 13, 2010

### iZH

Yes, thanks.
The question said, i need to change it to standard form.
Do you have any idea on how to convert 12000m/3600s to standard form?
This is the part which i actually stuck at.

By using scientific calculator, my calculator showed this
12000m/3600s = 3.33333 which is endless.
I found this is the wrong way to solve the question.

So i gave my try on the second method in mind.
converting 12000m to standard form give me 1.2 x 10(to the power of)4
converting 3600s to standard form give me 3.6 x 10(to the power of)3
Now i'm stuck at this step again.
1.2 x10(to the power of)4 / 3.6 x 10(to the power of)3
I can't seems to give the answer in standard form as i think this is the wrong way too.

So, any ideas on how to change the answer to standard form?

Last edited: Jan 13, 2010
8. Jan 13, 2010

### vela

Staff Emeritus
You just have to truncate the number at the correct number of significant figures. The original figure was 12 km/h, which has two significant figures, so the answer would be 3.3 m/s. If it had been 12.00 km/h, you'd write 3.333 m/s.

You don't need to include a power of 10 when the exponent would be zero.

9. Jan 13, 2010

### iZH

Ok, i get it now. Thanks for every effort you put in this thread :) Appreciate your help so much. ^^