20 N north because He is pushing it 20 newtons north.
Answer:
The correct option is (a).
Explanation:
We know that, the E is inversely proportional to the distance as follows :

We can write it as follows :

Put all the values,

So, the correct option is (a).
Answer: 
Explanation:
Centripetal acceleration
is calculated by the following equation:
Where:
is the Earth's orbital speed
is the orbital radius

Answer:
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Explanation:
The wave speed to this question is 400 meters