200 N
Given ;
Weight = 400 N
Length of the ladder = 10 m
Using the equation;
Torque = d x F, where F is the perpendicular force and d is the distance
Calculating torque about the lower end,
Tweight = Twall
400N(5cos30) = F (10sin30)
F = 200 N
Therefore, the magnitude of force exerted on the peg by the ladder is 200 N