Solved: PHYSICS Question for NEET

NEET PHYSICSEasy

In which of the following cases, a force will not be required to keep the particle in the given motion?

The particle is going in a circle

The particle is going along a straight line

The momentum of the particle is constant

The acceleration of the particle is constant

Newton's Second Law: The net external force acting on a particle is equal to the rate of change of its linear momentum ( $ec{F} = \frac{d ec{p}}{dt}$ ) [Source 57, 69].
Condition for No Force: For a force not to be required ( $ec{F} = 0$ ), the rate of change of momentum must be zero. This implies that the momentum $ec{p}$ must be constant ( $ec{p} = \text{constant}$ ).
Analyze Options:

Circular Motion: The direction of velocity changes continuously, meaning momentum changes. This requires a centripetal force [Source 66].
Straight Line: A particle can move in a straight line with changing speed (acceleration). If it accelerates, force is required ( $F=ma$ ).
Constant Acceleration: A constant non-zero acceleration implies a constant non-zero force ( $F=ma$ ) [Source 55].
Constant Momentum: This satisfies the condition $ec{F} = 0$ directly.

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