# D Alemberts principle - When is body in equilibrium position? - Theory of Machines - 1

Q.  According to D' Alembert's principle, the body is in equilibrium position if
- Published on 06 Aug 15

a. inertia force is applied in the direction opposite to the resultant force
b. inertia force is applied in the same direction of the resultant force
c. both a. and b.
d. none of the above

ANSWER: inertia force is applied in the direction opposite to the resultant force

#### Discussion

• Sravanthi   -Posted on 19 Oct 15
D' Alembert's principle

- According to D'Alembert's principle, resultant torque acting on the body with inertia torque keeps the body in equilibrium position.

- If resultant force passes through C.G. Of body, then according to Newton's law the equation is given as,

FR = ma

FR – ma = 0 ------------ FI =ma

If FI = –ma, then FR + FI = 0

Therefore, if inertia force is applied in the direction opposite to the resultant force, the body is in equilibrium position.

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