Answer: 0.577
Explanation: assume ladder makes angle theta with horizontal
forcing angle and weight w=10N
when ladder is about to slip the fractional force f its maximum value f=meuN
meu=coefficient of friction between ladder
perpendicular component N=Wcostheta,t=W sintheta
meu=(Ttanalpha)/N=(W sin theta tanalpha)/(w cos theta)=tantheta tanalpha
theta=30degree
alpha=60 degree
meu=tan30degree tan60degree=0.577