May 30, 2013

## What is the tension in the wire while the masses are in motion?

A 3.2 m long cylindrical steel wire with a cross-sectional diameter of 6.4 mm is placed over a frictionless pulley, with one end of the wire connected to a mass 6.6 kg and the other
end connected to a mass 3.3 kg. The acceleration of gravity is 9.8 m/s^2. Young’s modulus for steel Y = 2 X10^11 Pa.

**What is the tension in the wire while the masses are in motion? Answer in units of N.

**By how much does the wire stretch while the masses are in motion? Answer in units of mm.

?F = g(6.6-3.3) = 32.34 N
a = ?F/m = 32.34/(6.6+3.3) = 3.2667 m/s²

T = m1(g-a) = m2(g+a) = 43.12 N

?L = ?L/E = TL/AE = 43.12*3.2/[?/4(.0064²)*2E11] = 2.145E-5m = 2.145E-2 mm

## How do i calculate the hydroxide ion concentration in a saturated solution?

Please, i’ve been trying to do this one problem of my homework and I have no idea what I’m doing. I’ve looked through the notes, the book, everything. I just don’t get it.
The equation is Cr(OH)3(s) Cr 3+(aq) +3OH- (aq) and the Ksp -1.00 x10^-6.

Cr(OH)3(s) —> Cr3+(aq) +3OH- (aq)
First of all, ignore Cr(OH)3 when setting up Ksp because it is a solid.
You can set up an ice table:
(Ignore the solid) Cr3+ 3OH-
I 0 0
C +x +3x
E x 3x

Ksp = [Cr3+][OH-]^3
Therefore:
-1.00×10^-6 = (x)(3x)^3
-1.00×10^-6 = 27x^4
Pretty sure you can solve for x from there.
Remember that once you solve x to multiply it by 3 to get the concentrate of hydroxide (it was originally 3x according to the ICE table)