What is the magnitude of the downward force

[catmd13]

Homework Statement

80-kg man balances the boy on a teeter-totter as shown.
Note: Ignore the weight of the board. What is the magnitude of the downward force exerted on the fulcrum in Newtons?

Homework Equations

The Attempt at a Solution

 

[method_man]

Homework Statement

80-kg man balances the boy on a teeter-totter as shown.
Note: Ignore the weight of the board. What is the magnitude of the downward force exerted on the fulcrum in Newtons?[/b]

Perhaps like this. First we use momentum equations to determine boys weight.
ΣM=0 m_b*g*4=m_m*g*1
m_b=m_m1/4
m_b=80/4=20
Then we use forces equations.
ΣF=0 m_b*g+m_m*g-F_f
F_f=m_b*g+m_m*g
F_f=20*9,81+80*9,81
F_f=981 N

 

[nlightner]

The magnitude of the downward force exerted on the fulcrum in Newtons is equal to the weight of the 80-kg man plus the weight of the boy. Assuming the boy has a weight of 40 kg, the total downward force would be 120 kg (80 kg + 40 kg) or approximately 1176 Newtons (120 kg x 9.8 m/s^2). This is because the downward force exerted on the fulcrum is equal to the sum of all the forces acting on the teeter-totter, which includes the weight of the man and the boy.