What is the approximate weight of a 20.kg rock

[vaironl]

Since it has a decimal it would be 20kg * 9.8m/s which equals 196kg m/s^2 = 196N

But the decimal means i have to round two sig figs, which would make it 200N?

A very simple problem, I really don't know why I'm asking it.

 

[tiny-tim]

hi vaironl!

do you mean 20.0 kg ?

if so, that's three significant figures

 

[vaironl]

hi vaironl!

do you mean 20.0 kg ?

if so, that's three significant figures

Thanks for the reply, tim. "And let me say, that is a big post count"

My paper says 20.kg so I'm rounding to two significant figures. Am I right?

 

[tiny-tim]

i've no idea what "20.kg" means

i understand "20 kg" and "20.0 kg", but I've never seen "20.kg" or even "20. kg"

 

[Pengwuino]

Yes that is correct. When you see things like 20.kg, it means that the 0 is significant. If it were simply 20kg without the decimal, that would mean the number is only accurate to 1 significant figure. If, as tiny-tim advised, it were 20.0 kg, it would mean the second 0 is significant as well and there are 3 significant figures to take into account.

So your answer is 200N, accurate to 2 significant figures.

Scientific notation is really great because it clears these kind of odd notations. 20kg to 2 significant figures in SI notation would be 2.0 x 10^1 kg, clearly showing the 0 is significant.

 

[tiny-tim]

ah! thanks, Pengwuino!

 

[vaironl]

i've no idea what "20.kg" means

i understand "20 kg" and "20.0 kg", but I've never seen "20.kg" or even "20. kg"

Yes that is correct. When you see things like 20.kg, it means that the 0 is significant. If it were simply 20kg without the decimal, that would mean the number is only accurate to 1 significant figure. If, as tiny-tim advised, it were 20.0 kg, it would mean the second 0 is significant as well and there are 3 significant figures to take into account.

So your answer is 200N, accurate to 2 significant figures.

Scientific notation is really great because it clears these kind of odd notations. 20kg to 2 significant figures in SI notation would be 2.0 x 10^1 kg, clearly showing the 0 is significant.

Thanks, I knew something was going wrong. My teacher usually does things like that.
I can't believe sometimes he even gets about 3-6 problems incorrectly which demonstrates unprofessional work ethic.