A man of height 2 metres walks at a uniform speed of 5 km/hr away from a lamp post which is 6 metres high.Please Find the rate at which the length of his shadow increases.
let the length of the shadow be DE= y m .
and let the distance between the man and the lamppost be x m.
therefore dx/dt = 5km/hr
let AB be the height of lamppost and CD be the height of man. therefore
AB= 6 m and CD = 2m
by similar triangles,
now differentiating wrt time t.
hope this helps you.