An object of mass 4 kg falls from rest through a vertical distance of 20 m and reaches with velocity of 10 `(m)//(s)` on ground. How much work is done by air friction?

Explanation

To solve the problem of how much work is done by air friction on an object falling through a vertical distance, we can follow these steps:

### Step 1: Identify the known values
- Mass of the object (m) = 4 kg
- Distance fallen (d) = 20 m
- Final velocity (v) = 10 m/s
- Initial velocity (u) = 0 m/s (since it falls from rest)
- Acceleration due to gravity (g) = 10 m/s² (assuming standard value)
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