A person of mass 60 kg is standing on a spring balance inside a lift. If the lift falls freely downwards, then the reading of the spring balance will be equal to :

Question

Accepted Answer

When a person of mass 60 kg is standing on a spring balance inside a lift that is falling freely downwards, the reading of the spring balance will be zero. This is because both the person and the lift are in a state of free fall under the influence of gravity, experiencing the same acceleration due to gravity (approximately 9.8 m/s²). In this scenario, the person and the lift are accelerating downwards at the same rate, creating a condition known as "weightlessness."

1. **Explanation for Option 4 (Zero):**
   - In free fall, the only force acting on the person is gravity, and there is no normal force exerted by the spring balance on the person. The spring balance measures the normal force, which is the force exerted by a surface to support the weight of an object resting on it. Since the lift and the person are both accelerating downwards at the same rate, the normal force becomes zero. Consequently, the spring balance reads zero, indicating that the person is effectively "weightless" relative to the lift.

2. **Why Option 1 (Equal to 60 kg) is Incorrect:**
   - If the lift were stationary or moving at a constant velocity, the spring balance would read 60 kg, as it would measure the gravitational force acting on the person. However, in free fall, the normal force is zero, so the reading cannot be 60 kg.

3. **Why Option 2 (More than 60 kg) is Incorrect:**
   - The reading on the spring balance would be more than 60 kg if the lift were accelerating upwards, as this would increase the normal force. In free fall, there is no upward acceleration, so the reading cannot be more than 60 kg.

4. **Why Option 3 (Less than 60 kg) is Incorrect:**
   - A reading less than 60 kg would occur if the lift were accelerating downwards but not in free fall (e.g., descending with some resistance or deceleration). In free fall, the normal force is zero, not just reduced, so the reading is zero, not less than 60 kg.

In conclusion, during free fall, the spring balance reads zero because there is no normal force acting on the person, confirming that Option 4 is the correct answer.