Use of electromagnetic because it moves very faster than others for example xrays theynar very very slow so that not It it is d.
The frictional force is 39.4 N
Explanation:
We can solve this problem by applying Newton's 2nd law of motion: in fact, the net force acting on the block is equal to the product between its mass and its acceleration. So we can write

where
is the net force
m is the mass
a is the acceleration
Here we know that the box is moving with constant velocity, so its acceleration is zero:

This means that the net force is also zero:

The net force on the block is given by the applied force, forward, and the frictional force, backward:

where
is the applied force
is the frictional force
Therefore, solving for
,

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3rd number line -5- -4 is -9
also it’s math not physics or science
A) 
The magnitude of the capacitive reactance is given by

where
is the angular frequency
C is the capacitance
While the magnitude of the inductive capacitance is given by

where L is the inductance.
Since we want the two reactances to be equal, we have

So we find

B) 7449 rad/s
In this case, we have
is the inductance
is the capacitance
Therefore, substituting in the formula for the angular frequency, we find

C) 
Now we can us the formulas of the reactances written in part A). We have:
- Capacitive reactance:

- Inductive reactance:
