Answer:
The magnetic field in the region a < r < b is 
Explanation:
If we have the a < r < b. The formula of current is:

Where:
A = area enclosed by the loop.
Itotal = total current in loop.



If we have the Ampere`s law:

Answer: 25 km
Explanation: If it travels 25 km in 1 hour it is going 25 km/h meaning if its speed doesn't change for the next hour it will go another 25 km.
Answer:
4.5s
Explanation:
u=30m/s
v=50m/s
s=180m
a=constant(given)
By third equation of motion, v
2
=u
2
+2as
(50)
2
=(30)
2
+2a(180)
a=
3
40
m/s
2
By first equation of motion, v=u+at
50=30+(
9
40
)t
t=
2
9
=4.5sec
B - speed and direction are combined in another quantity, called velocity. It can be thought of as its speed in a particular direction. Speed is the corresponding scalar quantity, because it does not have a direction.