They are unproven but accepted as fact.
Many experiments support them but they can be disproven by the results of a single experiment. Until then, they stand.
The third statement is correct.
Answer:
The magnetic field is 
Explanation:
From the question we are told that
The mass of the metal is 
The current is 
The distance between the rail(length of the rod ) is 
The coefficient of kinetic friction is 
Generally the magnetic force is mathematically represented as

Given that the rod is moving at a constant velocity, it
=> 
Where
is the kinetic frictional force which is mathematically represented as

So

=> 
substituting values
=> 
=> 
Answer:
Explanation:
Force = (mass) · (acceleration)
= (1,000 kg) · (9.8 m/s²)
= 9,800 newtons