For a standing wave on a string, the wavelength is equal to twice the length of the string:

In our problem, L=50.0 cm=0.50 m, therefore the wavelength of the wave is

And the speed of the wave is given by the product between the frequency and the wavelength of the wave:
The formula of net Force is:
F = ma
where m is the mass of the object
a is the acceleration of the object
so if we triple the net force applied to the object:
3F = ma
a = 3F / m
so the acceleration will also be tripled. because from the equation, the force is directly proportional to the acceleration
B. they both involve wave interaction.
Answer:
Option B
Explanation:
Magnification of Microscope is

Mo= Magnification of objective lens and
Me= magnification of the eyepiece.
Both magnifications( of objective and eyepiece) are inversely proportional to the focal length.
Magnification,

when the focal length is less magnification will be high and when the magnification is the low focal length of the microscope will be more.
Thus. Magnification will increase by decreasing the focal length.
The correct answer is Option B i.e. using shorter focal length