Question #09151

1 Answer
Dec 11, 2016

M=34.9677M=34.9677 [kg]

Explanation:

Calling TT the tension on the rope, N_1N1 the normal force at the man floor, N_2N2 the normal force at the mass location, mu_sμs the friction coefficient, mm the man mass thetaθ the angle at the rope and gg the gravity, we have

Horizontally

T cos(theta)-mu_s N_1=0Tcos(θ)μsN1=0

Vertically

N_1-m g + T sin(theta)=0N1mg+Tsin(θ)=0 and T+N_2-M g=0T+N2Mg=0

but at the problem conditions we have N_2=0N2=0 so we have

{(T cos(theta)-mu_s N_1=0),(N_1-m g + T sin(theta)=0),(T-M g=0):}

Solving for T,N_1,M we obtain

((T = (g m mu_s)/(Cos(theta) + mu_s Sin(theta))),(N_1 = (g m Cos(theta))/(Cos(theta) + mu_s Sin(theta))),(M = (m mu_s)/(Cos(theta) + mu_s Sin(theta))))

So finally

M = (m mu_s)/(Cos(theta) + mu_s Sin(theta))=34.9677