An object is suspended from a spring balance in a lift. The reading is 240 N when the lift is at rest. If the spring balance reading now change to 220N, then the lift is moving

Options

A. Downward with constant speed
B. Downward with decreasing speed
C. Downward with increasing speed
D. Upward with increasing speed

Explanation

To solve the problem, we need to analyze the situation of an object suspended from a spring balance in a lift. The reading on the spring balance changes based on the motion of the lift.

### Step-by-Step Solution:

1. **Understanding the Initial Condition:**
- When the lift is at rest, the reading on the spring balance is 240 N. This indicates that the weight of the object (mg) is equal to the reading on the spring balance.
- Therefore, we can conclude that the actual weight of the object is:
\[ mg = 240 \, \text{N} \]

2. **Analyzing the Change in Reading:**
- When the lift is moving, the reading on the spring balance changes to 220 N. This indicates that the tension (T) in the spring balance is now less than the weight of the object.
- We have:
\[ T = 220 \, \text{N} \]

3. **Identifying the Motion of the Lift:**
- Since the reading on the spring balance (220 N) is less than the weight of the object (240 N), it suggests that the lift is accelerating downwards.
- According to Newton's second law, if the lift is moving downwards with increasing speed, the net force acting on the object can be expressed as:
\[ mg - T = ma \]
- Here, \(mg\) is the weight of the object, \(T\) is the tension (reading on the spring balance), and \(a\) is the acceleration of the lift.

4. **Calculating the Acceleration:**
- Rearranging the equation gives us:
\[ mg - T = ma \implies 240 \, \text{N} - 220 \, \text{N} = ma \implies 20 \, \text{N} = ma \]
- This means the net force acting on the object is 20 N, which is causing it to accelerate downwards.

5. **Conclusion:**
- Since the reading on the spring balance decreased from 240 N to 220 N, we conclude that the lift is moving downwards with increasing speed. Thus, the correct answer is that the lift is moving downwards with increasing speed.

### Final Answer:
The lift is moving downward with increasing speed.

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