We know that frequency is an inverse value of time
this implies that time is the inverse value of frequency
.
Now since <em>f</em> is <em>40kHz</em><em>,</em><em> </em>we can calculate period or duration for that matter time.

Hope this helps.
r3t40
Its d. the water isn't moving the fish, and that's how they remain stationary. they don't have any currents pushing on them. if this is wrong, its c, which is practically the same thing. but its most likely d.
Answer:
Explanation:
The speed of the water in the large section of the pipe is not stated
so i will assume 36m/s
(if its not the said speed, input the figure of your speed and you get it right)
Continuity equation is applicable for ideal, incompressible liquids
Q the flux of water that is Av with A the cross section area and v the velocity,
so,


the diameter decreases 86% so


Thus, speed in smaller section is 48.6 m/s
Frequency: 
Explanation:
The force experienced by an electron in a magnetic field is

where
is the electron charge
v is the speed of the electron
B is the strength of the magnetic field
Since the force is perpendicular to the direction of motion of the electron, the force acts as centripetal force, so we can write:

where
r is the radius of the orbit
is the mass of the electron
Re-arranging the equation,
(1)
We also know that in a circular motion, the speed is equal to the ratio between circumference of the orbit and orbital period (T):

Substituting into (1),

We also know that 1/T is equal to the frequency f, so

In this problem,

Therefore, the frequency of the electrons is

The concept required to perform this exercise is given by the coulomb law.
The force expressed according to this law is given by

Where,

q = charges of the objects
r= distance/radius
Our values are previously given, so

Replacing,



The force acting on the block are given by,




Therefore the box is accelerated upward.