A person is standing in an elevator. In which situation he finds his weight less ?

Options

A. When the elevator moves upward with constant acceleration
B. When the elevator moves downward with constant acceleration
C. When the elevator moves upward with uniform velocity
D. When the elevator moves downward with uniform velocity.

Explanation

To determine in which situation a person standing in an elevator finds his weight less, we need to analyze the different scenarios of elevator motion.

### Step-by-Step Solution:

1. **Understanding Weight in an Elevator**:
- The weight of a person is the force exerted on them due to gravity, which is given by \( W = mg \), where \( m \) is the mass of the person and \( g \) is the acceleration due to gravity.

2. **Elevator Moving Upward with Constant Acceleration**:
- When the elevator moves upward with constant acceleration \( a \), the effective force acting on the person is:
\[ N = mg + ma \]
- Here, \( N \) is the normal force (apparent weight), which is greater than the actual weight \( mg \). Thus, the person feels heavier.

3. **Elevator Moving Downward with Constant Acceleration**:
- When the elevator moves downward with constant acceleration \( a \), the effective force acting on the person is:
\[ N = mg - ma \]
- In this case, since \( ma \) is subtracted from \( mg \), the normal force \( N \) (apparent weight) is less than the actual weight \( mg \). Thus, the person feels lighter.

4. **Elevator Moving Upward or Downward with Uniform Velocity**:
- If the elevator moves with uniform velocity (either upward or downward), the acceleration \( a = 0 \). Therefore, the normal force is:
\[ N = mg \]
- In this case, the person feels their normal weight, as there is no change in the effective force acting on them.

### Conclusion:
The situation in which the person finds his weight less is when the elevator is moving downward with constant acceleration. Thus, the correct answer is option B.

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