Force of gravity of chain links problem

[dois]

Homework Statement

Two chain links are connected together and are suspended by a string. The mass of the top link, link#1 is 8kg, while the mass of the second/bottom link #2 is unknown. If an applied force on the string attached to link #1 of 216N[up], and the links experience an acceleration of 2m/s^2 [up] find the mass of link #2 and the force that link#2 exerts on link1
The only given variables we have are
a= 2 m/s^2
Fa= 216N
g=10N

I'm guessing I have to isolate variables, but I am not sure what equations to use.

 

[Delphi51]

Use F = ma where F is the total of the forces on the object.
You must be very clear in your mind what "the object" is. The conventional approach is to do an F = ma for each object and the force of one link on the other then will appear in both equations - you get a system of two equations to solve. Sometimes you can reduce the work by cleverly thinking of the two objects combined as one object and use just one F = ma.

 

[dois]

Would the total of the forces on the object just be the applied force which is 216?

 

[Delphi51]

How about gravity?

 

[dois]

oh right, so then F, being the total of all the forces would be...
216N + 10N
so F=226N

 

[Delphi51]

No, that 10 N is incorrect. In your first post,

g=10N

should read g = 9.81 m/s².
The force of gravity is mg, which you can't immediately find because you don't know m. Anyway, it is better to stick with symbols like m until you have solved the equation for the quantity you want to find.