Correct Option
The correct option is$mg$
Explanation
According to Newton's First Law of Motion, an object moving at a constant velocity has zero acceleration. For an object to maintain zero acceleration, the net external force acting on it must be zero (equilibrium condition).
Detailed Analysis
To lift an object vertically upwards, two primary forces act on it:
- Gravitational Force (Weight): Acting downwards, with a magnitude of $W = mg$, where $m$ is the mass and $g$ is the acceleration due to gravity.
- Applied Force ($F$): Acting vertically upwards.
For the object to move at a constant velocity, the net force must be zero ($F_{net} = 0$). This implies that the upward applied force must exactly balance the downward gravitational force.
$$F_{\text{up}} = F_{\text{down}}$$
$$F = mg$$
Therefore, the minimum magnitude of force required is $mg$.
Key Takeaway: Moving an object at a constant velocity requires a net force of zero. The applied force must simply counteract the opposing force (gravity), making it equal to the object's weight ($mg$).