B. I think is the correct answer
        
             
        
        
        
Answer:
562.5J
Explanation:
The following were obtained from the question:
F = 45N
d = 12.5m
w =? 
The work done can be achieved by using 
w = F x d 
w = 45 x 12.5 
w = 562.5J 
 
        
             
        
        
        
Take into account that in a standing wave, the frequency f of the points executing simple harmonic motion, is simply a multiple of the fundamental harmonic fo, that is:
f = n·fo
where n is an integer and fo is the first harmonic or fundamental.
fo is given by the length L of a string, in the following way:
fo = v/λ = v/(L/2) = 2v/L
becasue in the fundamental harmonic, the length of th string coincides with one hal of the wavelength of the wave.
 
        
             
        
        
        
Answer:
1.82 rad/s².
Explanation:
Applying,
α = (ω₂-ω₁)/t..................... Equation 1
Where α = angular acceleration of the fan blades, ω₂ = final angular velocity of the fan blades, ω₁ = initial angular velocity of the fan blades, t =  time.
Given: ω₂ = 350 rpm = (350×0.1047) rad/s = 36.645 rad/s. ω₁ = 250 rpm = (250×0.1047) rad/s = 26.175 rad/s, t = 5.75 s.
Substitute into equation 1
α = (36.645-26.175)/5.75
α = 10.47/5.75
α = 1.82 rad/s².
Hence the magnitude of the angular acceleration of the fan blades = 1.82 rad/s²