In this problem, we need to solve for Bubbaâs mass. To do this, we let A be the area of the raft and set the weight of the displaced fluid with the raft alone as ÏwAd1g and ÏwAd2g with the person on the raft, where Ïw is the density of water, d1 = 7cm, and d2= 8.4 cm. Set the weight of displaced fluid equal to the weight of the floating objects to eliminate A and Ïw then solve for m.
ÏwAd1g = Mg
ÏwAd2g = (M + m) g
d2âd1Â = (M + m)/g
m = [(d2âd1)-1] M = [(8.4 cm/7.0 cm) - 1] (600 kg) =120 kg
This means that Bubbaâs mass is 120 kg.