Why were you able to see the effects of the magnetic fields using iron filings

Iron filing are soft magnetic materials. The are highly attracted by magnets. 
They are used in the study of magnetic fields.
Another reason why they are used because they are light and and they can aline themselves in the paths of the magnetic fields. This way the fields patterns can be seen clearly.

P = 60 W

Explanation: Power is the ratio of energy per unit time. Energy can also be substituted by work.

P = W / t

= 30 N ( 10 m) / 5.00 s

= 60 W