e , V
5
d
dt =
m3/h and h = 4 m Therefore
5 =
(4)2
4
dh
dt
π
⋅
or
dh
dt  = 5
35
22
m/h
4
88
7


=
π =

π


Thus, the rate of change of water level is 35 m/h
88 Example 32 A man of height 2 metres walks at a uniform speed of 5 km/h away from
a lamp post which is 6 metres high