An anemometer for measuring wind speed consists of four small metal cups, each o

Question

An anemometer for measuring wind speed consists of four small metal cups, each of 120g, mould on the ends of rods of mass 80g and 32cm long. Find the anemometer's rotational inertia about its central axis. The cups can be treated as point masses. The thin rod's rotational moment is Irod = 1/12mL2. Determine the angular momentum when it's spinning at constant angular velocity 12 rev/s in the direction indicated in the figure. L = I. omega. Suppose the wind exerts a force of 2.5N on each cup, what is the frictional torque which balances the torque created by the wind

Explanation / Answer

a) I = 2* Irod + 4*Icup= 2*1/12*(80/1000)*(32/100)^2 + 4*(120/1000)*(32/100)^2=0.05052 b) L = Iw = 0.05052*(12*2*pi)=3.809 c) Since 4 cups torque = 4 r F = 4*(32/100)*2.5=3.2

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