The linear density of the rope is, ρ=0.5kg∕m The mass of the rope is, m=ρ×l =0.5×4 =2kg The total mass of the system is, M=48+2=50kg The figure below represents the free body diagram.
a=
F
M
=
25
50
=0.5
m
s2
The force acting on the block is, f=ma =48×0.5 =24N