Question
What is the length of the pipe?
Answer:
(a) 0.52m
(b) f2=640 Hz and f3=960 Hz
(c) 352.9 Hz
Explanation:
For an open pipe,  the velocity is given by

Making L the subject then

Where f is the frequency,  L is the length,  n is harmonic number,  v is velocity
Substituting 1 for n,  320 Hz for f and 331 m/s for v then

(b)
The next two harmonics is given by
f2=2fi
f3=3fi
f2=3*320=640 Hz
f3=3*320=960 Hz
Alternatively,  and
 and 
 
(c)
When v=367 m/s then

 
        
             
        
        
        
You are trying to convert mass to volume. That ain't working
        
             
        
        
        
Either A or D. If I were answering I'd go with my git answer and say A
        
             
        
        
        
Explanation:
It is given that,
A planet were discovered between the sun and Mercury, with a circular orbit of radius equal to 2/3 of the average orbit radius of Mercury.
Mass of the Sun, 
Radius of Mercury's orbit, 
Radius of discovered planet, 

Let T is the orbital period of such a planet. Using Kepler's third law of planetary motion as :




T = 4135214.625 s
or
T = 47.86 days
So, the orbital period of such a planet is 47.86 days. Hence, this is the required solution.
 
        
             
        
        
        
-- You've GOT the kinetic energy of the bullet. 
-- That's the amount of work that has to be done to stop it.
-- work = (avg force) x (penetration) and they just gave you the average force.
-- Did you think it would be this easy ?