Okay so don't quote me on this but I believe the answer is A) I'm saying this because B and C make no sense. and you can't change the mass of something without changing it totally.
Answer:
Volume of each grain of sand:

radius of the spherical grain is given,

The grains are made up of silicon dioxide.
The density is equal to 
Then, the mass of each grain is given by:

#1
For closed pipe the fundamental frequency will be given as




#2
For open pipe the wavelength for Nth harmonic will be given as


#3
for a closed pipe the frequency is given as

here for third harmonic n = 3

now plug in all values



#10
since in the given figure there are three complete loops
so in this case the <em>number of harmonics are THREE</em>
Answer:
F = 10.8N
Explanation:
Given the mass m = 0.4kg, v1 = 25m/s, v2 = 12m/s and t =0.5s
From Newtown's second law of motion the average force can be found. This law states that the product of the force experienced by a body and the time t of the force acting on the body is equal to the change in momentum of the body. Mathematically it can be stated as follows
F×t = m(v2 – v1)
F = m(v2 – v1)/t = 0.4(25 – 12)/0.5 = 10.8N