In a string of length L, the wavelength of the n-th harmonic of the standing wave produced in the string is given by:
The length of the string in this problem is L=3.5 m, therefore the wavelength of the 1st harmonic of the standing wave is:
The wavelength of the 2nd harmonic is:
The wavelength of the 4th harmonic is:
It is not possible to find any integer n such that 
, therefore the correct options are A, B and D.
A coil of insulated wire around an iron core
Pressure is measured as force per unit area, which is the third option.
<h3>What is pressure?</h3>
Pressure is amount of force that is applied over a given area divided by the size of this area.
Pressure is calculated by multiplying the force applied on the object by the area covered.
Since force is measured in Newtons (N) and area is measured in m², the unit of pressure is Nm².
Therefore, pressure is measured as force per unit area.
Learn more about pressure at:
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Since power = work done/time, 60= work done/120, work done = 120*60 = 7200. So,work done = 7200N (Newton).
I'm not sure if you're supposed to convert the seconds to time.
