When air is blown into the open pipe,
L = 
where nis any integral number 1,2,3,4 etc. and λ is the wavelength of the oscillation
⇒λ=
Note here that n=1 is for fundamental, n=2 is first harmonic and so on..
⇒ third harmonic will be n=4
Given L=6m, n=4, solving for λ we get:
λ=
=3m
Relationship of frequency(f), velocity of sound (c) and wavelength(λ) is:
c=f.λ Or f= 
⇒f=
≈115 Hz
Your answer for this question is the third option.
The strength of the gravitational force between two objects depend on two factors, mass and distance.
Answer: a. net force is acting on object A in the same direction of its motion.
Explanation:
The second law of Newton states that the acceleration of a particular object is dependent on two main things which are the mass and force. According to the law, the acceleration of the object will be directly related to the net force while the acceleration is also relates inversely to the mass.
Therefore, based on the information given in the question, a force is acting on object A in the same direction of its motion.
