Question

A body is acted upon by two forces each of magnitude $F$, but in opposite directions. State the effect of the forces if both forces act at the same point of the body. Which of the following is/are true?

• A. Resultant force $=0$
• B. Moment of forces $=0$
• C. No motion
• D. All of the above

Answer 1

Answer: (D)

All of the above

Here, we are applying two force in same magnitude but in opposite that is one is F and -F. Hence resultant force is $F+(-F)=0$.

Hence, resultant force is zero. Here perpendicular distance is same for both the forces.

Hence, if we calculate $r\times F$ cross product. We get the same magnitude of moments but opposite in direction as force are of opposite in direction. Hence moments are also zeroes. Without any resultant and moment there will be no motion.