Answer :
Answer:
Explanation:
This is the case of forced oscillation . The pendulum having the same or matching time period or angular frequency with that of angular frequency of external periodic force , will be in resonance having largest amplitude.
Angular frequency of pendulum having length .9 m
= [tex]\sqrt{\frac{g}{l } }[/tex]
l = .9
angular frequency
= [tex]\sqrt{\frac{10}{0.9 } }[/tex]
= 3.33 rad / s
If we calculate angular frequencies of pendulum of all lengths given , we will find that other lengths do not give angular frequency falling between 2 and 4 radian . So only pendulum having length of .9 m will have vibration of maximum amplitude.