Question

7 Someone is trying to balance a (110cm) plank with certain forces. a) Calculate the moment of the 60N force (about O), then name its type. b) Calculate the moment of the 30N force (about O), then name its type c) Will the plank balance? If not, which way will it tip? d) What extra force would be needed at (B) to balance the plank?

Answer 1

(a) 30 Nm. Clockwise moment

(b) 15 Nm Anti clockwise

(c) Not balance, it tip to the clockwise direction

(d) 150 N

Step-by-step explanation:

Assumimg the diagram attached is required to complete the question,

(a) Moment of 60 N force (about O) is

Moment = Force(F)× perpendicular distance (d)

M₁ = F₁d₁................ Equation 1

From the diagram, F₁ = 60 N, d₁ = 50 cm = 0.5 m

M₁ = 60×0.5

M₁ = 30 Nm. Clockwise moment.

(b) The moment of the 30 N force (about O) is given as

M₂ = F₂d₂

From the diagram, F₂ = 30 N, d₂ = 50 cm = 0.5 m

M₂ = 30×0.5

M₂ = 15 Nm Anti clockwise

(c) The plank will not balance because the sum of clockwise moment is not equal to the sum of anti clock wise moment. It tip to the clockwise direction.

(d) From the diagram,

Applying the principle of moment,

Sum of clockwise moment = sum of anti clockwise moment.

30(0.5)+X(0.1) = 60(0.5)

15+0.1X = 30

0.1X = 30-15

0.1X = 15

X = 15/0.1

X = 150 N.