I believe it is the first one
Special relativity led the path for general relativity; special relativity is in a sense a special application of the rules of general relativity. While general relativity is in position to tackle all of these problems, special relativity can tackle only problems in inertial frames. Inertial frame means that the frame of reference is inot accelerating. So, we disqualify answers A and D. However, remember that moving in a circle means that there is an acceleration, the centrifugal one, even if the speed does not change. Hence C is also incorrect.
The correct answer is B, since if there is no change in velocity, the frame does not accelerate and it is inertial.
1) a) attract
The magnetic force between two magnetic poles is attractive for two unlike poles and repulsive for two like poles. Therefore we have:
1- For two north poles, the force between them is repulsive
2- For two south poles, the force between them is repulsive
3- For a north pole and a south pole, the force between them is attractive
In this problem, we are in the situation described in 3), so the force between the poles is attractive.
2) a) motion of electrons
While electric fields are produced by static electric charges, magnetic fields are produced by charges in motion (currents). In particular, a current in a wire (where a current is simply the motion of electrons inside the wire) produces a magnetic field whose intensity is

where
I is the current in the wire
r is the radial distance from the wire
And the direction of the field lines are such that the field form concentric circles around the wire.
Using a=f/m u get 100 bc 5/.05 =100m/s
Answer:
20
27
Explanation:
Given parameters:
Atomic mass = 47
Atomic number = 20
Unknown:
Number of protons = ?
Number of neutrons = ?
Solution:
To solve this problem,
Atomic mass = number of protons + number of neutrons
Atomic number = number of protons
So;
Number of protons = 20
Now;
Number of neutrons = Atomic mass - number of protons
Number of neutrons = 47 - 20 = 27