Problem 16P

Three children are trying to balance on a seesaw, which consists of a fulcrum rock, acting as a pivot at the center, and a very light board 3.6 m long (Fig. 9–50). Two playmates are already on either end. Boy A has a mass of 50 kg, and girl B a mass of 35 kg. Where should girl C, whose mass is 25 kg, place herself so as to balance the seesaw?

FIGURE 9–50

SolutionStep 1 of 3 The momentum is quantity of measurement of motion of object.Mathematically, p=mv In an isolated system , the total momentum is conserved because there is noexternal force acting on it .Consider two bodies Initial momentum of the bodies before collision p and p resp1ctively 2 final momentum of the bodies after collision p 1 and p 2 respectivelyFrom newton's second lawF= dp dt Force exerted on 1 by 2 ,F = p1 1 12 t p2 2 Force exerted on 2 by 1 ,F = 21 t By newton's third lawF =-F 12 21p p (p p ) t 1= t 2 p 1- p 1(p 2- p )2 p 1- p 1p 2+ p 2 p - p =p + p 1 2 1 2 p = p f i\n