A ladder, 5 meter long, standing on a horizontal floor, leans against a vertical wall. If the top to the ladder slides down wards at the rate of 10 cm/sec, then find the rate at which the angle between the floor and ladder is decreasing when lower end of ladder is 2 meters from the wall.
Given that 
. We have to find 
when h=2m
Also 
– (1)
At b=2m, 
Differentiating (1) with respect to t, we get
Substituting values, we get
⇒ 
1