A girl of height $120 c m$ is walking away from the base of a lamp-post at a speed of $0.6 m / s e c$ . If the lamp is $3.6 m$ above the ground level, then find the length of her shadow after $4$ seconds

1.2 m

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1.5 m

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1.8 m

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2.2 m

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Solution

The correct option is A $1.2 m$
R.E.F image
Given the height of
girl $= 1.2 m$
lamp post $= 3.6 m$
girl is moving with velocity (V) = 0.6m/s away
from lamp post
$∴$ distance travelled by girl after 4 second is
$x = 0.6 \times 4 = 2.4 m$
By concept of Similar triangles
$\frac{1.2 m}{3.6 m} = \frac{y}{x + y} \Rightarrow 1.2 (2.4 + y) = 3.6 y$
$\Rightarrow 2.4 = 2 y$
$y = 1.2 m$ (ie, length of shadow after 4 seconds)

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A girl of height 120 cm is walking away from the base of a lamp-post at a speed of 0.6 m/sec. If the lamp is 3.6 m above the ground level, then find the length of her shadow after 4 seconds

A girl of height $120 c m$ is walking away from the base of a lamp-post at a speed of $0.6 m / s e c$ . If the lamp is $3.6 m$ above the ground level, then find the length of her shadow after $4$ seconds