A body of mass 5 kg is placed in a lift. Find the reaction between the floor of the lift and the body when the lift moves upward: i) at constant velocity ii) with an acceleration of 2.5 m s⁻² (take g

The mass of the body is $m = 5 \text{ kg}$.
The acceleration due to gravity is $g = 10 \text{ m s}^{-2}$.
Since the velocity is constant, the acceleration of the lift is $a = 0 \text{ m s}^{-2}$.

The reaction force is $\boxed{\textbf{50 N}}$.

The mass of the body is $m = 5 \text{ kg}$.
The acceleration due to gravity is $g = 10 \text{ m s}^{-2}$.
The acceleration of the lift is $a = 2.5 \text{ m s}^{-2}$.

The reaction force is $\boxed{\textbf{62.5 N}}$.

:
A body of mass $5 \text{ kg}$ is placed in a lift. If the lift moves upward with a retardation of $2 \text{ m s}^{-2}$, find the reaction between the floor of the lift and the body (take $g = 9.8 \text{ m s}^{-2}$).

When a lift moves upward with retardation (deceleration), the effective acceleration is downwards. The formula for the reaction force $R$ becomes $R = m(g-a)$, where $a$ is the magnitude of the retardation.

The mass of the body is $m = 5 \text{ kg}$.
The acceleration due to gravity is $g = 9.8 \text{ m s}^{-2}$.
The retardation of the lift is $a = 2 \text{ m s}^{-2}$.

The reaction force is $\boxed{\textbf{39 N}}$.