# What is the approximate weight of a 20.kg rock

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.

Related Other Physics Topics News on Phys.org
tiny-tim
Homework Helper
hi vaironl! do you mean 20.0 kg ?

if so, that's three significant figures 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
Homework Helper
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
Gold Member
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.

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
Homework Helper
ah! thanks, Pengwuino! 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.