Answer:
Here is the complete question:
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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.
Answer:
force-strength,power or energy as an attribute of motion, movement or action. Example: Frictional force.
Answer:

Explanation:
Given that
Mass of rifle = M
Initial velocity ,u= 0
Mass of bullet = m
velocity of bullet = v
Lets take final speed of the rifle is V
There is no any external force ,that is why linear momentum of the system will be conserve.
Initial linear momentum = Final linear momentum
M x 0 + m x 0 = M x V + m v
0 = M x V + m v

Negative sign indicates that ,the recoil velocity will be opposite to the direction of bullet velocity.
Answer:
The steps are outlined in the explanation below.
Explanation:
The average velocity is derived midpoint from the initial to the final velocity. Here is the proof:
Find the total displacement:
let the displacement be given by the letter s
Then since the average velocity is defined as: 
where t = final time
t₀ = initial time
v = final speed
v₀ = initial time
where x denotes the position, then

where v =
and dx = change in distance with respect to time.