Question

A person carries a plank of wood 2.00 m long with one hand pushing down on it at one end with a force f1 and the other hand holding it up at .500 m from the end of the plank with force f2 . if the plank has a mass of 20.0 kg and its center of gravity is at the middle of the plank, what are the magnitudes of the forces f1 and f2 ?

Answer 1

Answer:

F₁ = 4,120.2 N

F₂ = 3,924N

Explanation:

1) Balance of angular momentum around the end where F₁ is applied.

F₂ × 0.5m - F₁ × 0 = mass × g × 1m

⇒ F2 × 0.5 m= 20 kg × 9.81 m/s² × 1 m = 1,962 N×m

F₂ = 196.2 Nm / 0.5m = 3,924 N

2) Balance of forces

F₁ - F₂ = mg

F₁ = F₂ + mg = 3,924N + 20kg (9.81 m/s²) = 4,120.2 N