Question

A girl of height 90cm is walking away from the base of a lamp post at a speed of 1.2m/sec .If the lamp post is above the ground ,find length of her shadow after 4 seconds

Answer 1

Answer:

=>>160

Step-by-step explanation:

Let the girl of height be at point D on the ground from the lamp post after 4 seconds. Therefore,

AD=1.2 m/sec ×4 sec =4.8 m =480 cm

Suppose the length of the shadow of the girl be x cm when she at position D. Therefore,

BD=x cm

In ∆BDE and ∆BAC,

∠BDE=∠BAC (90°)

∠DBE=∠ABC (Common)

Thus, ∆BDE∼∆BAC (AA similarity)

BE/BC =DE/AC =BD/AB

( Corresponding sides are proportional )

90/360 = x/480+x

⇒4x=480+x

⇒4x−x=480

⇒3x=480

⇒x= 480/3

=>>160

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