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Force and Laws of Motion — Science STD 9 — Question

Gujarat BoardEnglish MediumSTD 9ScienceForce and Laws of Motion1 Mark
MCQ
When will a body under the action of several forces have $0$ acceleration?
  • ✓
    When the vector sum of all the forces acting on the body is zero
  • B
    When a body is very heavy
  • C
    When the body is very light
  • D
    When the body is a point body
✓

Answer

Correct option: A.
When the vector sum of all the forces acting on the body is zero
Referring formula $F=ma$
Thus acceleration will be zero, when resultant force is zero. In option $(d),$ the point body is to be considered.
A point body does not mean a body of zero mass. A point body or a particle is ideally a piece or quantity of matter having practically no linear dimensions but only a position.
The measure of this quantity of matter is the mass of the particle.
It is a usual convention to imagine bodies as point objects when we are only concerned about their mass and not about the distribution of mass.
Thus earth can be considered as a point body when we describe its motion about sun.

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