The unstretched length of spring AB is 2.8 m . If the block is held in the equilibrium position shown, determine the mass of the block at D.

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To determine the mass of the block at D, we need to consider the forces acting on the block in the equilibrium position.

In the given diagram, we can identify the following forces:
1. The weight of the block acting downwards.
2. The force exerted by the spring, which is directed upwards.

In equilibrium, the sum of the forces acting on the block must be zero. Therefore, we can set up the following equation:

Forces upwards - Forces downwards = 0

Let's break it down further:

1. Forces upwards:
- The force exerted by the spring. We can use Hooke's Law to express this force as F = -kx, where F is the force, k is the spring constant, and x is the displacement from the equilibrium position.
- We are given the unstretched length of the spring (2.8 m). In the equilibrium position, the spring is stretched by a length of x = AB = 2.2 m.
- Since the force exerted by the spring is directed upwards, we take it as a positive value.

Forces upwards = +kx

2. Forces downwards:
- The weight of the block. The weight (force due to gravity) can be calculated using the formula W = mg, where W is the weight, m is the mass, and g is the acceleration due to gravity.
- Since weight acts downwards, we take it as a negative value.

Forces downwards = -mg

Now, we can set up the equation:

+kx - mg = 0

To solve for the mass of the block (m), we need to know the spring constant (k) and the displacement (x). Unfortunately, these values are not provided in the given information or diagram. Therefore, we cannot determine the mass of the block at point D based on the given information.

If you have access to additional information such as the spring constant or the displacement, please provide it so that we can help you calculate the mass of the block at point D.