Solving Horizontal Force Problems Involving Blocks

[jarny]

Homework Statement

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?

Homework Equations

Fnet=m*a

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

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?

 

[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 ...

 

[jarny]

Thank very much

 

[jarny]

Wait how would I found F->


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


Then F->= 17 N?

 

[LowlyPion]

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

 

[jarny]

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

 

[LowlyPion]

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

Isn't a the acceleration of both blocks?

And total mass is Ma + Mb.

So ...

 

[jarny]

Thanks