The velocity of the wave on the string is given by

Solving the above equation,

The frequency of the wave
and wave length is 
The velocity is 
Substituting numerical values,

The length of the string is 
I believe the answer is gravitational force
The atmospheric P is greater than the P in the flask, since
the Hg level is lacking down lower on the side open to the atmosphere.
43.4 cm x (10 mm / 1 cm) = 435 mm
the density of Hg is 13.6 / 0.791 = 17.2 times better than the liquid in the
manometer. This means that 1 mmHg = 17.2 mm of manometer liquid.
435 mm manometer liquid x (1 mm Hg / 17.2 mm manometer liquid) = 25.3 mm
Hg
The pressure in the flask is 755 - 25.3 = 729.7 mmHg.
729.7 mmHg x (1 atm / 760 mmHg ) = 0.960 atm.
I believe the correct answer from the choices listed above is the second option. In a nuclear power plant, nuclear energy is first changed to thermal energy. Heat energy is first given off in this process. Hope this answers the question. Have a nice day.