Question

figure shows a uniform rod of length ---

Answer 1

See the diagram.

Draw the free body diagrams first.

Since the rod has uniform density, m2 = 2 * m1.
 
Let F be the force on mass m1 by the mass m2. Let the entire rod be moving with an acceleration a.

     So  32 - 20 = (m1+m2)* a
                        =  3 m1 * a
  => m1 * a = 4 Newtons.

For m1,
        F - 20 N = m1 * a = 4
=>    F = 20 + 4 = 24 Newtons.

24 N is the answer

Answer 2

your correct answer is 24 Newton