A, Lenz' Law. There need to be a difference of flux, so if you use AC you will get a current too.
Answer:

Explanation:
Mass of block=10 kg
Applied horizontal force =F=20 N
Friction force=f=10 N
We have to find the acceleration of block.
Net force=Applied horizontal force-friction force

Where F= Horizontal force
f=Friction force
m=Mass of object
a=Acceleration of object


Hence, the acceleration of the block=
Answer:
10000 J or 10 KJ
Explanation:
power = workdone/time taken
400 = workdone/25
workdone = 400 * 25
=10000 J