Respuesta :
Answer:
M = 281.25 lb*ft
Explanation:
Given
Wman = 150 lb
Weight per linear foot of the boat: q = 3 lb/ft
L = 15.00 m
Mmax = ?
Initially, we have to calculate the Buoyant Force per linear foot (due to the water exerts a uniform distributed load upward on the bottom of the boat):
∑ Fy = 0 (+↑) ⇒ q'*L - W - q*L = 0
⇒ q' = (W + q*L) / L
⇒ q' = (150 lb + 3 lb/ft*15 ft) / 15 ft
⇒ q' = 13 lb/ft (+↑)
The free body diagram of the boat is shown in the pic.
Then, we apply the following equation
q(x) = (13 - 3) = 10 (+↑)
V(x) = ∫q(x) dx = ∫10 dx = 10x (0 ≤ x ≤ 7.5)
M(x) = ∫10x dx = 5x² (0 ≤ x ≤ 7.5)
The maximum internal bending moment occurs when x = 7.5 ft
then
M(7.5) = 5(7.5)² = 281.25 lb*ft
The maximum internal bending moment of the given balance system is; 281 lb.ft
How to find bending moment?
We are given;
Weight of man; W_m= 150 lb
Weight per linear foot of the boat: q = 3 lb/ft
Length of boat; L = 15 m
Summing forces about the y-axis from the given diagram of the boat gives;
∑Fy = 0
⇒ q'*L - W - q*L = 0
⇒ q' = (W + q*L)/L
⇒ q' = (150 lb + (3 lb/ft * 15 ft))/15 ft
q' = 13 lb/ft
Thus;
Net weight per linear foot;
q(x) = (13 - 3) = 10
Shear force is;
V(x) = ∫q(x) dx = ∫10 dx = 10x (0 ≤ x ≤ 7.5)
Bending moment is;
M(x) = ∫10x dx
M(x) = 5x² (0 ≤ x ≤ 7.5)
The maximum internal bending moment occurs when x = 7.5 ft.
Thus;
M(7.5) = 5(7.5)² = 281 lb.ft
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