# The Concurrent Forces Viva Questions and Answers

The Concurrent Forces Viva Questions and Answers

(i) State parallelogram law of forces

Ans: If two forces acting at a point be represented in magnitude and direction by the adjacent sides of a parallelogram drawn from a point, the resultant force is represented in magnitude and direction by the diagonal of the parallelogram drawn from the same point

(ii) State triangle of forces

Ans: If three forces acting at a point can be represented in magnitude and direction by the sides of a triangle taken in order then the forces is in equilibrium,

(iii) What is meant by resultant of a set of force?

Ans: It is that single force which effectively replaces the set of forces

(iv) What are concurrent forces?

Ans: Forces acting at a point are known as concurrent forces.

(v) What is Lami's theorem?

Ans: If three forces acting at a point keep it in equilibrium, then each force is proportional to the since of the angle between the other two.

(vi)
What is the angle between them

Ans: 45°

vii) Will the forces 15N, 20N and 40N acting at a point keep it in equilibrium?

Ans: No

viii) What are the main sources of error in the experiment?

Ans: (a) Friction at the pulleys. (b) Thread cannot be weight less.

(ix) If there is a lot of friction at the pulleys in what way the result of this experiment be affected?

Ans: The forces represented by the hanging weight will have values lower than what are given by the relation W = mg

(x) Apparatus of Concurrent Forces

Ans: Parallelogram law apparatus consisting of two frictionless pulleys attached to a framework fixed on the top of a vertical drawing board, light inextensible strings, weights and weight hangers and the given body.

(xi) Theory of Concurrent Forces

Ans: If three co-planer concurrent forces P, Q and R keep a point in equilibrium, the resultant of P and Q will be equal and opposite to R, the equilibrant.