• Support PF! Buy your school textbooks, materials and every day products Here!

Dimensional analysis. Please check my working

  • #1

Homework Statement


Two spheres are cut from a certain uniform rock. One has radius 4.30 cm. The mass of the other is six times greater. Find its radius.


Homework Equations


v = (4/3)(pi)(r)^3
m = vp


The Attempt at a Solution


6[(4/3)(pi)(r1)3] = (4/3)(pi)(r2)3
8(pi)(r1)3 = (4/3)(pi)(r2)3
6(r1)3 = (r2)3
6(4.3)(1/3) = 9.7568

Answer:
9.76 cm

I got this question wrong for some reason... Where is my mistake...?
 

Answers and Replies

  • #2
rude man
Homework Helper
Insights Author
Gold Member
7,764
760


6(r1)3 = (r2)3
6(4.3)(1/3) = 9.7568

Answer:
9.76 cm

I got this question wrong for some reason... Where is my mistake...?


Going from 2nd last to last equation you made your basic mistake.
 
  • #4
SteamKing
Staff Emeritus
Science Advisor
Homework Helper
12,796
1,667
If you take a sphere with radius r, and make another sphere with radius 2*r, what is the ratio of the volume of the bigger sphere to the smaller sphere?
 
  • #5
rude man
Homework Helper
Insights Author
Gold Member
7,764
760
I don't see it... :(
Take the cube root of each side. Your mistake is on the left-hand side.
Fact: (ab3)1/3 = a1/3b
 

Related Threads on Dimensional analysis. Please check my working

  • Last Post
Replies
2
Views
10K
  • Last Post
Replies
2
Views
1K
  • Last Post
Replies
1
Views
5K
  • Last Post
Replies
2
Views
1K
Replies
7
Views
2K
Replies
6
Views
1K
  • Last Post
Replies
5
Views
1K
  • Last Post
Replies
5
Views
1K
Replies
9
Views
1K
Top