5–111. a box having a weight of 8 lb is moving around in a circle of radius ra = 2 ft with a speed of (va)1 = 5 ft> s while connected to the end of a rope. if the rope is pulled inward with a constant speed of vr = 4 ft> s, determine the speed of the box at the instant rb = 1 ft. how much work is done after pulling in the rope from a to b? neglect friction and the size of the box.

16. a brave but inadequate rugby player is being pushed backward by an opposing player who is exerting a force of 800 n on him. the mass of the losing player plus equipment is 90.0 kg, and he is accelerating at 1.20m/s2 size 12{1 "." "20"" m/s" rsup { size 8{2} } } {} backward. (a) what is the force of friction between the losing player’s feet and the grass? (b) what force does the winning player exert on the ground to move forward if his mass plus equipment is 110 kg? (c) draw a sketch of the situation showing the system of interest used to solve each part. for this situation, draw a free-body diagram and write the net force equation.