- #1
Roderic Day
- 1
- 0
Homework Statement
http://img53.imageshack.us/img53/6141/41622697.png
Homework Equations
F = ma, all that basic stuff.
The Attempt at a Solution
Alright
g = 32.2
Ma = 150/g = 4.66lb
Mb = 75/g = 2.33lb
so Box A
__
|...}==== 2T
|__|
box B
3T
-----|...|______ 60lb
===={__|
Sum of Fx = ma
so for A
2T = 4.66aA
for B
60 - 3T = 2.33aB
then for the lengths of the wire I did
_________
O________
...n__O
|-sa-||sb|
so L = 2sa + 3sb
0 = 2aA + 3aB
but clearly aA and aB must have opposite signs so
2aA = 3aB
using simultaneous equations with the following you get
60 = 2.33aB +3T
0 = 4.66(3/2)aB - 2T
which makes aB = 7.22ft s-2 (ANS)
and T = 14.4 lb
then i figured there were two ways to go about work done
KEi(A+B) + Wd = KEf(A+B)
or Wd = 2T*sA + (60-3T)*sB
Which is great cause you get to doublecheck your result
the problem is that for method 1 I get 334.1J
and for method 2 I get 216.6J
So, yeah, any help is appreciated.
EDIT1: Formatting Errors
EDIT2: I found my mistake. My simultaneous eqs were wrong, it was 6.99, not 4.99.
Now the answers are aA = 7.02 ft s-2 and W = 140.4J
I'd still appreciate some double-checking on my method since I'm not really sure if I'm doing this right.
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