To determine the minimum size of nylon rope required to lift a weight of 3.5 tonnes using a watch tackle, accounting for frictional losses, we need to go through a few key steps.

Given Information:

• Weight to lift: 3.5 tonnes (equivalent to 3500 kg)
• Friction loss: 12% of the load per sheave (pulley)

Step 1: Calculate the total force required, including friction losses.

If 12% of the load is lost per sheave, we need to consider how many pulleys (sheaves) are in the system. However, the total friction force will be additive based on the number of pulleys. Let's assume $n$ pulleys.

Each sheave adds an additional force requirement equal to $12\%$ of the current load.

• Force required for one pulley: $\text{Force on one sheave} = 3500 \times 1.12 = 3920 \, \text{kg}$

• For $n$ pulleys, the force would increase depending on how many pulleys are present. If there are multiple pulleys, we'd adjust this accordingly.

Step 2: Determine the