# 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.

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