Questions 16 and 17 refer to the information and diagram below.
Jonathan is using a rope to lift a box with Becky in it; the box is hanging off the side of a bridge, Jonathan is on top. A rope is hooked up from the box and passes a fixed railing; Jonathan holds the box up by pressing the rope against the railing with a massless, frictionless physics textbook. The static friction coefficient between the rope and railing is $\mu_{s}$; the kinetic friction coefficient between the rope and railing is $\mu_{k}<\mu_{s}$; the mass of the box and Becky combined is $M$; and the initial height of the bottom of the box above the ground is $h$. Assume a massless rope.
What magnitude force does Jonathan need to exert on the physics book to keep the rope from slipping?
Answer Choices
A. M g
B. \mu_{k} M g
C. \mu_{k} M g / \mu_{s}
D. \left(\mu_{s}+\mu_{k}\right) M g
E. M g / \mu_{s}