Question

A weightless ladder 20 ft long rests against a frictionless wall at an angle of 60° from the horizontal. A 150 pound man is 4 ft from the top of the ladder. A horizontal force is needed to keep it from slipping. Choose the correct magnitude from the following.(a) 175 lb(b) 100 lb(c) 120 lb(d) 17.3 lb

Answer 1

Answer:- 175 lb

OA = 2 sin 60 = 1.732

MN = 4 cos 60 = 2

W = 150 pounds

Taking moment at A,

F x OA = W x MN

F = ( W x MN) / OA

Substituting W , MN & OA  in above.

So, F = 175 lb