Three forces acting on a rigid body are represented in magnitude, direction and line of action by the three sides of a triangle taken in order. The forces are equivalent to a couple whose moment is equal to
A. Area of the triangle
B. Twice the area of the triangle
C. Half the area of the triangle
D. None of these
Answer: Option B
This Question Belongs to Mechanical Engineering >> Engineering Mechanics
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The resultant of two equal forces P making an angle $$\theta ,$$ is given by
A. $$2{\text{P}}\sin \frac{\theta }{2}$$
B. $$2{\text{P}}\cos \frac{\theta }{2}$$
C. $$2{\text{P}}\tan \frac{\theta }{2}$$
D. $$2{\text{P}}\cot \frac{\theta }{2}$$
A. Equal to
B. Less than
C. Greater than
D. None of these
If a number of forces are acting at a point, their resultant is given by
A. $${\left( {\sum {\text{V}} } \right)^2} + {\left( {\sum {\text{H}} } \right)^2}$$
B. $$\sqrt {{{\left( {\sum {\text{V}} } \right)}^2} + {{\left( {\sum {\text{H}} } \right)}^2}} $$
C. $${\left( {\sum {\text{V}} } \right)^2} + {\left( {\sum {\text{H}} } \right)^2} + 2\left( {\sum {\text{V}} } \right)\left( {\sum {\text{H}} } \right)$$
D. $$\sqrt {{{\left( {\sum {\text{V}} } \right)}^2} + {{\left( {\sum {\text{H}} } \right)}^2} + 2\left( {\sum {\text{V}} } \right)\left( {\sum {\text{H}} } \right)} $$
A. $${\text{a}} = \frac{\alpha }{{\text{r}}}$$
B. $${\text{a}} = \alpha {\text{r}}$$
C. $${\text{a}} = \frac{{\text{r}}}{\alpha }$$
D. None of these
Akhilesh Chauhan it says three forces acting on a body... It doesn't mean that line of action of all the three forces are acting on the body coincides at a point.
And if three forces are represented by three sides of a triangle taken in order then resultant force may be zero but couple may not be zero...
Since three forces acting on a rigid body are represented in magnitude, direction and line of action by the three sides of a triangle taken in order that means the body is in equilibrium. So the total force as well as moment will be zero.
This can also be explained as"
(1) The resultant of any two forces will be equal in magnitude, opposite to the direction and along the line of action of the remaining third force. So again resultant is zero and since both the resultant of two forces and third force are passing through a single point, moment of the forces will be zero.
(2) Since the three forces forming a triangle, so all the three are passing through a single point, so moment of the forces is equal to zero.
So option D should be correct.
Plz explain