When work done by force of gravity is negative, then

Options

A. PE increases
B. KE increases
C. PE remains constant
D. PE decrease

Explanation

To determine when the work done by the force of gravity is negative, we can analyze the relationship between the direction of the gravitational force, the displacement of the object, and the work done.

### Step-by-Step Solution:

1. **Understand Work Done by a Force**:
Work done (W) by a force is given by the formula:
\[ W = F \cdot d \cdot \cos(\theta) \]
where \( F \) is the force, \( d \) is the displacement, and \( \theta \) is the angle between the force and the displacement vector.

2. **Identify the Force of Gravity**:
The force of gravity acts downwards towards the center of the Earth. Therefore, the gravitational force \( F_g \) can be represented as:
\[ F_g = mg \]
where \( m \) is the mass of the object and \( g \) is the acceleration due to gravity.

3. **Consider the Direction of Displacement**:
- When an object moves **upward** (against the gravitational force), the displacement \( d \) is in the opposite direction to the force of gravity. In this case, \( \theta = 180^\circ \), so:
\[ W = mgd \cdot \cos(180^\circ) = -mgd \]
This means the work done by gravity is **negative** when the object is moving upward.

4. **Analyze the Case of Downward Movement**:
- Conversely, when an object moves **downward**, the displacement \( d \) is in the same direction as the gravitational force. Here, \( \theta = 0^\circ \), so:
\[ W = mgd \cdot \cos(0^\circ) = mgd \]
In this scenario, the work done by gravity is **positive**.

5. **Conclusion**:
Therefore, the work done by the force of gravity is negative when the object is moving **upward**. This is because the gravitational force acts in the opposite direction to the displacement.

### Summary:
- Work done by gravity is negative when the object moves upward.
- Work done by gravity is positive when the object moves downward.