Answer:(a)10 ft/s
(b)4 ft/s
Explanation:
Given
height of light 
height of man

From diagram



differentiate both sides

Tip of shadow is moving at the rate of

(b)rate at which length of his shadow is changing
Length of shadow is 
differentiating w.r.t time


Stratosphere because the atmosphere get denser
Jj thomas' model contained electrons.
The current model contains a nucleus with electrons orbiting around it. :)
<h2>
Number of revolutions required to travel 100 yards is 57.</h2>
Explanation:
Diameter of tire,D = 20 inches
Perimeter of tire = πD
Perimeter of tire = π x 20 = 62.8 inches
Distance traveled = 100 yards
1 yard = 36 inches
Distance traveled = 100 x 36 = 3600 inches
In one revolution it travels 62.8 inches.

Number of revolutions required to travel 100 yards is 57.