A stone is dropped from certain height above the ground. After 5 s a ball passes trhough a pane of glass held horizontally and instantaneously loses `20%` of its velocity. If the ball takes 2 more seconds to reach the ground the height of the glass above the ground is

Explanation

To solve the problem step by step, we will follow the given information and apply the relevant physics concepts.

### Step 1: Determine the initial conditions
The stone is dropped from a height, so its initial velocity (U) is 0 m/s. The acceleration due to gravity (g) is approximately 10 m/s².

### Step 2: Calculate the velocity of the stone after 5 seconds
Using the equation of motion:
\[ V = U + g \cdot t \]
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