# Intro Physics question

Hootenanny
Staff Emeritus
Gold Member

You must have some idea as to where to start. We can't help you unless you at least attempt the problem first.

Well my professor hasn't given any examples yet on this and I can't find any in my textbook either. I was hoping someone could give me pointers on where to start.

lewando
Homework Helper
Gold Member
You can start by looking on the interweb for things like "measuring the diameter of a molecule".

I haven't done any physics or math in over a year which is probably why I'm having trouble with pretty basic problems.

Here's my attempt:

(a) Area of slick = $\pi$r2
diameter of slick = 2x1010
volume of slick= area x thickness
volume of oil=volume of slick= 1L = 0.001m3

0.001m3=($\pi$r2
r=1261.57m
d=2523m

(b) $\rho$=M/V
V=$\pi$r3
=$\pi$(1x10-10)3
V=3.14x10-30m3
M=850kg/m3 x 3.14x10-30m3

M=2.67x10-27kg

does that make sense?

lewando
Homework Helper
Gold Member
(a) Area of slick = $\pi$r2
diameter of slick [you mean thickness of slick] = 2x1010
volume of slick= area x thickness
volume of oil=volume of slick= 1L = 0.001m3

0.001m3=($\pi$r2
r=1261.57m
d=2523m
Looks okay, too many significant digits though.

(b) $\rho$=M/V
V=$\pi$r3
=$\pi$(1x10-10)3
V=3.14x10-30m3
M=850kg/m3 x 3.14x10-30m3

M=2.67x10-27kg

does that make sense?
V=$(4/3)\pi$r3

Thank you!

The diamete/thickness was a typo, I wrote it properly on my sheet :)

As for the significant digits, does 2.5x103m work?

lewando
Homework Helper
Gold Member
If you are using a number like 2x10-10, I think one SD would suffice.