# Homework Help: Force Problem with weights

1. Jun 4, 2010

### Motorboar

1. The problem statement, all variables and given/known data
A series of weights connected by very light cords are given an upward acceleration of 4.00 m/s2 by a pull P, as shown in Fig. 5.3.( a verticle strand of 4 balls with mass 5,10,15,and 20 kg with the pull at the top) A, B, and C are the tensions in the connecting cords.
the pull P is closest to:

290 N
690 N
50 N
200 N
490 N

2. Relevant equations
F= ma

3. The attempt at a solution
treating the weights as one mass
Pull-mg=ma
pull=m(a+g)
= 552
Which is not one of the answers. What is the error in my logic?

2. Jun 4, 2010

### collinsmark

I'm don't see an error in your logic (if I'm interpreting your description of the figure correctly). Maybe there's an error in your calculations? :uhh: What did you use for m and g?

[Edit: In other words, your equations seem fine. But I don't know why you ended up with 552]

3. Jun 4, 2010

### Motorboar

added the masses wrong xD Thank you.