The free body diagram for the wooden block is shown below
Using the condition of the equilibrium,
In the
x-direction, the summation of all the forces is to be zero.
f−T=0 µR−T=0 T=0.5R...(i)
In the
y-direction, , the summation of all the forces is to be zero.
T+R−90=0 ⇒0.5R+R−90=0 R=60N Hence, the normal force on the wooden block is
60N Using the Eq. (i),
T=0.5(60)=30N Hence, the maximum value of the tension in the rope,
so that wooden block will not move is
30N.