-- During the time the ball is flying from the high roof to the low roof,
it's going to fall (100-25) = 75 meters.
How long does it take an object dropped from rest to fall 75 meters ?
Distance = (1/2) · (gravity) · (time)²
75 m = (4.9 m/s²) · (time)²
Time² = (75 m) / (4.9 m/s²)
Time² = 15.31 sec²
Time = √(15.31 sec²) = 3.91 seconds
So the ball has to cover the horizontal distance of 20 meters
in 3.91 seconds.
Distance = (speed) · (time)
20 m = (speed) · (3.91 sec)
Speed = (20 m) / (3.91 sec)
Speed = 5.11 m/s
(a) The lowest frequency (called fundamental frequency) of a wire stretched under a tension T is given by

where
L is the wire length
T is the tension
m is the wire mass
In our problem, L=10.9 m, m=55.8 g=0.0558 kg and T=253 N, therefore the fundamental frequency of the wire is

b) The frequency of the nth-harmonic for a standing wave in a wire is given by

where n is the order of the harmonic and f1 is the fundamental frequency. If we use n=2, we find the second lowest frequency of the wire:

c) Similarly, the third lowest frequency (third harmonic) is given by