# Two boxs

1. Feb 16, 2009

### jarny

1. The problem statement, all variables and given/known data

In Figure 5-50a, a constant horizontal force F->a is applied to block A, which pushes against block B with a 23.0 N force directed horizontally to the right. In Figure 5-48b, the same force is applied to block B; now block A pushes on block B with a 11.0 N force directed horizontally to the left. The blocks have a combined mass of 12.0 kg. What are the magnitudes of (a) their acceleration in Figure 5-50a and (b) force F->a?

2. Relevant equations

Fnet=m*a

http://edugen.wiley.com/edugen/courses/crs1650/art/qb/qu/c05/fig05_50.gif

3. The attempt at a solution

Ok so for block scenario one I have to find the Fnet to solve for m*a.
So I have Fnet= sum of forces=m*a

for case two

Fnet= sum of forces =m*a

So I have

12*a= Fapp+23-F_AB
12*a=Fapp-11+F_AB

I am stuck right here any tips?

2. Feb 16, 2009

### LowlyPion

Write down what you know.

Ma + Mb = 12

23N = Mb*a

11N = Ma*a

Since a is the same, then

Mb/Ma = 23/11

Mb = 12 - Ma = 23/11*Ma

Ma = 12*11/34 ...

3. Feb 16, 2009

### jarny

Thank very much

4. Feb 16, 2009

### jarny

Wait how would I found F->

Do I use: 23=F-> + X and 11=F-> -X ?

Then F->= 17 N?

5. Feb 16, 2009

### LowlyPion

What is your total mass and the acceleration of the system?

6. Feb 16, 2009

### jarny

So the F->applied would be 12*a which I found?

7. Feb 16, 2009

### LowlyPion

Isn't a the acceleration of both blocks?

And total mass is Ma + Mb.

So ...

8. Feb 16, 2009

Thanks