The normal reaction on a body placed in a lift moving up with constant acceleration `2ms^(-1) ` is 120 N. Mass of the body is (Take `g = 10ms^(-2)`)

Options

A. 10 kg
B. 15 kg
C. 12 kg
D. 5 kg

Answer

To solve the problem, we will use the concepts of forces acting on the body in the lift.

### Step-by-Step Solution:

1. **Identify the Forces**:
- The body experiences two forces:
- The gravitational force acting downwards: \( F_g = mg \)
- The normal force acting upwards: \( N \)

2. **Consider the Lift's Acceleration**:
- The lift is moving upwards with a constant acceleration \( a = 2 \, \text{m/s}^2 \).

3. **Apply Newton's Second Law**:
- When the lift accelerates upwards, the effective force acting on the body can be expressed as:
\[ N = mg + ma \]
- Here, \( N \) is the normal force, \( mg \) is the weight of the body, and \( ma \) is the additional force due to the lift's acceleration.

4. **Substitute Known Values**:
- We know from the problem that \( N = 120 \, \text{N} \), \( g = 10 \, \text{m/s}^2 \), and \( a = 2 \, \text{m/s}^2 \).
- Substitute these values into the equation:
\[ 120 = mg + m(2) \]
- This simplifies to:
\[ 120 = m(10 + 2) \]
- Which can be written as:
\[ 120 = m(12) \]

5. **Solve for Mass \( m \)**:
- Rearranging the equation gives:
\[ m = \frac{120}{12} \]
- Calculating this gives:
\[ m = 10 \, \text{kg} \]

### Final Answer:
The mass of the body is \( 10 \, \text{kg} \).