Answer:
1.29 N
Explanation:
The equation for force (with work and distance) is:

We can plug in the given values into the equation:

Answer:
Here is the complete question:
https://www.chegg.com/homework-help/questions-and-answers/magnetic-field-372-t-achieved-mit-francis-bitter-national-magnetic-laboratory-find-current-q900632
a) Current for long straight wire 
b) Current at the center of the circular coil 
c) Current near the center of a solenoid 
Explanation:
⇒ Magnetic Field due to long straight wire is given by (B),where

Plugging the values,
Conversion
,and 

⇒Magnetic Field at the center due to circular coil (at center) is given by,
So 
⇒Magnetic field due to the long solenoid,
Then
So the value of current are
,
and
respectively.
C is the awnser because c is single replacement
Kinetic Energy = 1/2 * m * v²
1/2 * 30 * 20²
1/2 * 30 * 400
12000/2
6000 J.