Q. 34.2( 32 Votes )

A girl of height 90 cm is walking away from the base of a lamp post at a speed of 1.2m/sec. If the lamp post is 3.6 m above the ground, find the length of her shadow after 4 seconds.

Answer :

Given, a girl with height 90cm and speed 1.2m/sec


And the lamp post is 3.6m above


Need to find the length of her shadow after 4sec



Consider Δ ABC and Δ DEC


ABC = DEC = 90°


ACB = DCE


Δ ABC Δ DEC


By converse proportionality theorem if a line divides any two sides of a triangle in the same ratio then the line must be parallel to the third side.


we have




x + 4.8 = 4x


4x – x = 4.8


3x = 4.8


X =


X = 1.6m


CE = 1.6m


Hence, the length of her shadow after 4 sec is 1.6m


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