Question

A lamp of negligible height is placed on the ground 'h' metre away from a wall. A man "I" metre tall is walking at a speed of l/10 m/sec. from the lamp to the nearest point on the wall. When he is mid-way between the lamp and the wall, the rate of change in the length of this shadow on the wall is.

aaj se sb ladke ban mera babu kisi se km hai kya ​

Answer 1

Since, the two triangles are similar,

l

1

h

=

x

l

2

⇒h=

x

l

1

l

2

⇒

dt

dh

=−

x

2

l

1

l

2

dt

dx

(As h is decreasing)

Given, x=

2

l

1

and

dt

dx

=

10

l

1

So,

dt

dh

=−

5

2l

2

m/sec

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