Length of the plank l = 4 m.
Height of the inclined plane, h = l m.
Mechanical advantage of the inclined plane is
`M.A. =(l)/(h)=(4m)/(1m)`
M.A. = 4
By definition, M.A. is equal to `=("load (L)")/("effort (E) ")`
`rArr 4 = (48N)/(E)`
`:. E = (48N)/(4)`
`E = 12N`