What is the smallest number of whole logs (rho = 715 kg/m3, radius = 0.0815 m, length = 2.76 m) that can be used to build a raft that will carry four people, each of whom has a mass of 84.0 kg?

n = 9 logs

Explanation:

given,

dimension of whole logs

ρ = 715 kg/m³

radius = 0.0815 m

length = 2.76 m

Weight of 4 people

W = 4 m g

W = 4 x 84 x 9.8

W = 3292.8 N ... (1)

Weight of logs

L = n x ρ V g

L = n x 715 x π x 0.0815²x 9.8 x 2.76

L = 403.56 n ... (2)

now, equating both the equation (1) and (2)

3292.8 = 403.56 n

n = 8.159

n = 9 logs

so, 9 logs will be used to carry 4 People of 84 Kg.