Question

Two people are carrying a uniform wooden board that is 3.00 m long and weighs 160 N.

If one person applies an upward force equal to 60 N at one end, at what point does the other person lift? Begin with a free-body diagram of the board.

Answer 1

Weight of the wooden board = W = 160 N

Length of the wooden board = L = 3 m

Upward force applied by the first person = F₁ = 60 N

Upward force applied by the second person = F₂

Balancing the forces on the wooden board,

W = F₁ + F₂

160 = 60 + F₂

F₂ = 100 N

The wooden board is uniform therefore the center of gravity of the wooden board lies at it's center.

Distance of the second person from the first person = D

Taking moment balance about the left end of the board.

W(L/2) = F₂D

(160)(1.5) = (100)D

D = 2.4 m

The other person has to lift at a point 2.4 m from the end where the first person is lifting the wooden board.