Question

8 Example 12: A 20 ft long 75 lb plank is lying on a frozen pond (There is no friction between the ice and the wood.). The Plank’s left end rests against the pier and a 200 lb man is standing on its right end 20 ft from the pier. How far from the pier is the left end of the plank after the man has walked from the right end to the left end of the plank?

Answer 1

let xcm is the initial distance between center of mass to pier.

xcm = (75*10 + 200*20)/(75 + 200)

= 17.3 ft

let x is the distance between left end of the plank after the man has walked from the right end to the left end of the plank.

so, x is the distance between pier and man.

final coardinate of center of mass = initial coardinate of center of mass

xcm' = xcm (because there is no net force)

(200*x + 75*(x+10))/(200 + 75) = 17.3

x = 14.6 cm <<<<<<---------------Answer