A lift is moving downwards with an acceleration equal to acceleration due to gravity. A body of mass m kept on the floor of the lift is pulled horizontally. If the coefficient of friction is 0.4, then the frictional resistance offered by the body is

Options

A. m g
B. `mu` mg
C. `2 mu mg`
D. Zero

Explanation

To solve the problem, we need to analyze the situation of the body in the lift that is accelerating downwards with an acceleration equal to the acceleration due to gravity (g).

### Step-by-Step Solution:

1. **Understanding the Situation**:
- The lift is moving downwards with an acceleration (a) equal to g.
- A body of mass \( m \) is placed on the floor of the lift.
- The coefficient of friction (\( \mu \)) between the body and the floor is given as 0.4.

2. **Determine the Effective Gravity**:
- When the lift accelerates downwards with an acceleration equal to g, the effective acceleration due to gravity (\( g_{\text{effective}} \)) acting on the body inside the lift becomes:
\[ g_{\text{effective}} = g - a = g - g = 0 \]
- This means that the body experiences no effective weight in the lift.

3. **Calculate the Normal Force**:
- The normal force (\( N \)) acting on the body is equal to the effective weight of the body. Since \( g_{\text{effective}} = 0 \):
\[ N = m \cdot g_{\text{effective}} = m \cdot 0 = 0 \]

4. **Calculate the Frictional Force**:
- The frictional force (\( F_f \)) can be calculated using the formula:
\[ F_f = \mu \cdot N \]
- Substituting the value of \( N \):
\[ F_f = 0.4 \cdot 0 = 0 \]

5. **Conclusion**:
- The frictional resistance offered by the body is \( 0 \).

### Final Answer:
The frictional resistance offered by the body is \( 0 \).

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