How many people can the raft hold before they start getting their feet wet, assuming the average person has a mass of 63 kg ?

Question

A raft is made of 15 logs lashed together. Each is 62 cm in diameter and has a length of 5.6 m . Do not neglect the weight of the logs. Assume the specific gravity of wood is 0.53.

Answer 1

The volume of 15 logs = 25.36 m^3

Density of water = 997 kg/m^3

If the logs are just fully covered with water, the buoyant force (up) = 247,784.3 N

The downward force from the weight of the logs = 131,324.7 N

So the people on the raft must makeup the difference 247,784.3-131,324.7 = 116,459.6 N

Since each person ha a weight of 617.4 N, then 116,459.6/617.4 = 188.6 Or

It would take 189 people in order to get their feet wet!