Question

A wind farm generator uses a two-bladed propeller mounted on a pylon at a height of 20 m. The length of each propeller blade is 12 m. A tip of the propeller breaks off when the propeller is vertical. At that instant, the period of the motion of the propeller is 1.2 second. The fragment files off horizontally, falls and strikes the ground at point P.

In figure, the distance from the base of the pylon to the point where the fragment strikes the ground is closest to -

• A. 120 m
• B. 130 m
• C. 140 m
• D. 160 m

Answer 1

Answer: (D)

160 m

Answer 2

x = v₀ t

h = $\frac{1}{2}$gt²

t = $\sqrt{\frac{2h}{g}}$= $\sqrt{\frac{2 \times 32}{10}}$ = $\frac{8}{\sqrt{10}}$

v₀ = wr = $\frac{2\pi}{T}$× 12 = $\frac{2\pi}{1.2} \times 12$= 20p

x = 20p × $\frac{8}{\sqrt{10}}$

$\frac{160 \times 3.14}{3.162}$

x = 160 m