Answer: 4 ft/s
Explanation:
Given
height of man
speed of person 
height if street light
Let x be the distance between person and street light and y be the length of his shadow
From diagram
as the two triangle ADE and ABC are similar therefore we can say that




differentiate above Equation w.r.t time we get


Answer:
The height will be 4 times.
Explanation:
Given that,
The speed at the bottom of the hill doubled.
We need to calculate the height
Using conservation of energy




Therefore,

Here, m and g are constant
Hence, The height will be 4 times.
magnetic field due to a finite straight conductor is given by

here since it forms an equilateral triangle so we will have

also the perpendicular distance of the point from the wire is

now from the above equation magnetic field due to one wire is given by



now since in equilateral triangle there are three such wires so net magnetic field will be
