A lift is moving down with an acceleration equal to the 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 `mu` then the frictional resistance offered by the body is:

Options

A. `mu Mg`
B. Mg
C. Zero
D. `mu` Mg/2

Answer

To solve the problem, we need to analyze the forces acting on 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. **Identify the Forces Acting on the Body:**
- The weight of the body (W) acting downwards is given by \( W = mg \), where \( m \) is the mass of the body and \( g \) is the acceleration due to gravity.
- The normal force (N) acting upwards on the body from the floor of the lift.

2. **Understand the Acceleration of the Lift:**
- The lift is accelerating downwards with an acceleration \( a = g \). This means that the effective acceleration acting on the body inside the lift is zero because the body is in free fall along with the lift.

3. **Calculate the Normal Force (N):**
- According to Newton's second law, the net force acting on the body in the vertical direction is given by:
\[ F_{net} = mg - N \]
- Since the lift is accelerating downwards at \( g \), the net force is also equal to the mass times the acceleration of the body, which is zero in this case (as both the lift and the body are falling together):
\[ F_{net} = 0 \]
- Therefore, we can set up the equation:
\[ mg - N = 0 \]
- Rearranging gives us:
\[ N = mg \]

4. **Determine the Normal Force in the Context of the Lift's Acceleration:**
- However, because the lift is accelerating downwards at \( g \), the effective normal force acting on the body becomes:
\[ N = mg - mg = 0 \]

5. **Calculate the Frictional Force:**
- The frictional force (f) can be calculated using the formula:
\[ f = \mu N \]
- Since we have found that \( N = 0 \), substituting this into the equation gives:
\[ f = \mu \cdot 0 = 0 \]

6. **Conclusion:**
- Therefore, the frictional resistance offered by the body is \( 0 \).

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

---