A 4-M-Long Ladder (Mass $= 56 \mathrm {~kg}$ ) Leans Against a Frictionless Wall

Multiple Choice

A 4-m-long ladder (mass $= 56 \mathrm {~kg}$ ) leans against a frictionless wall. The base of the ladder makes an angle $\theta$ with the rough floor $\left( \mu _ { s } \right)$ . If $\mu _ { s } = 0.5$ , the minimum value of $\theta$ , such that the ladder will not slip, is

A) 45º.
B) 56º.
C) 61º.
D) 72º.