UPSEE Solved Model Paper 7

The corresponding figure is shown below:

Here.
AB = x : distance covered by the edge of the shadow in time t
BC = y : distance covered by the man in lime t
In ΔACE,
tan θ =

CE

AB+BC

=

H

z+y

Similarly in ΔEFD,
tan θ =

ED

FD

=

H−h

Y

Since the angle ’θ' is same, we have

H

x+y

=

H−h

y

⇒ Hy = Hx + Hy - xh - yh
⇒ yh = Hx - xh
⇒ yh = x (H - h)
⇒

x

y

=

h

H−h

... (i)
Let v be the velocity of the edge of the shadow on the ground. Then
x = vt ... (ii)
and y = ut ... (iii)
substituting the values from eqs (ii) and (iii) in eq (i) we get

vt

ut

=

h

H−h

⇒ v =

hu

H−h

Hence, option 'A' is correct.