Kinematics Question 341
Question: A man of height h walks in a straight path towards a lamp post of height H with velocity v. Then velocity of the edge of the shadow on the ground will be
Options:
A) $ \frac{hv}{H+h} $
B) $ \frac{Hv}{H-h} $
C) $ \frac{H+h}{Hv} $
D) $ \frac{( H-h )}{Hh} $
Show Answer
Answer:
Correct Answer: B
Solution:
as $ \Delta LOS $ and $ \Delta MPS $ are similar so, $ \frac{H}{x}=\frac{h}{x-y}\Rightarrow ( H-hz )x=Hy $
$ \Rightarrow ( H-h )\frac{dx}{dt}=H\frac{dy}{dy}=Hv $
$ \Rightarrow V _{S}=\frac{Hv}{H-h} $
