Remark
You have to pick a velocity for an ultra sound wave. I'm going to take the sound velocity to be 331 m/s in air, because I'm assuming that is what is meant: it is the sound a bat would make once he emits the ultrasound to a microphone like device that receives it. The media through which that happens is air.
Givens
v = 331m/s
f = 4 *10^4 hz
Formula
velocity = wavelength * frequency
v =
*f
331/(4*10^4) = 
0.008275 = 
8.275*10^-3 = 
Answer:
Angular acceleration of the barrel is 0.011 rad/s².
Explanation:
It is given that,
Initial speed of the barrel ride = 0
Final speed of the barrel ride, 
On converting rev/sec to rad/sec as :
Since, 1 revolution = 2π radian
So, 
Time, t = 7.26 s
We need to find the angular acceleration of the barrel during that time. It is given by :



So, the angular acceleration of the barrel is 0.011 rad/s². Hence, this is the required solution.
Answer:
C. 352.0 kg-m/s
Explanation: Took the test on APEX
The speed of sound at a temperature of 56°C is 365.2 m/s