Question

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

Answer 1

⚫ Let AB Represent the lamp Post of height
3. 6m
⚫ The Girls Walk at a speed of 1. 2 m/s

⏩ In 4 Seconds She walks 4 × 1. 2 m = 4. 8 m
And reaches D.

⏩ let CD represent the girl of height 0.9 m
and DE is her shadow of x metre.

Now, in ∆CDE and ∆ ABE

∆CDE = ∆ ABE... Each 90°
E. = E Common
=> ∆ CDE - ∆ ABE AA Similarity Criterion.

=> DE/BE = CD/AB

⏩ X/X+4. 8 = 0. 9/3. 6
⚫ 4x = x + 4. 8
4x-x = 4. 8
3x. = 4. 8
X = 4. 8/3
⏩ X. = 1. 6 m.

So, length of the shadow after 4 seconds = 1. 6 m.