Arun
Last Activity: 6 Years ago
h=2 m, H=5 m, v=7 m/s u=?
x is the distance of man to lamp post,
y is the distance from the tip of the shadow to the lamp post.
From the similar triangles
H/h = y/(y-x),
5/2 = y/(y-x),
5y -5x=2 y,
3 y=5 x,
0.6 y=x,
d{0.6 y}/dt=dx/dt,
0.6(dy/dt)=dx/dt,
0.6u =v,
u=v/0. 6=7/0.6=11.66 m/s.
