Answer:
4.1 m
Explanation:
10 kW = 10000 W
20mi/h = 20*1.6 km/mi = 32 km/h = 32 * 1000 (m/km) *(1/3600) hr/s = 8.89 m/s
The power yielded by the wind turbine can be calculated using the following formula

where
is the air density, v = 8.89 m/s is the wind speed, A is the swept area and
is the efficiency



The swept area is a circle with radius r being the blade length



The answer to this statement is true!
Length of the pipe = 0.39 m
Number of harmonics = 3
Now there are 3 loops so here we can say


now here at the center of the pipe it will form Node
we need to find the distance of nearest antinode
So distance between node and its nearest antinode will be


So the distance will be 6.5 cm
I'm not entirely sure but I would think it's A.
I would say B : main sequence is the answer . this is the answer i believe because the star will increase in size and than shine brightly and when it's done , it will get smaller turning into nebula , eventually exploding sometime around the last stage , but not the last stage of b , c, or d
i really hope that this helps you a lot.