Most likely B. Will erode, if not it will grow weeds
Space surrounding magnet is called the magnetic field. In this field we can encounter magnetic force. Magnet attraction occurs when poles are unlike and is caused by magnetic force. It means that poles should have opposite values.
Answer:
v = 31.32 [m/s]
Explanation:
To solve this problem we must use the principle of energy conservation, which tells us that potential energy is converted into kinetic energy or vice versa. The potential energy can be calculated by the product of mass by gravity by height.

where:
Epot = potential energy [J]
m = mass = 25 [kg]
g = gravity acceleration = 9.81 [m/s²]
h = elevation = 50 [m]
Now replacing:
![E_{pot}=25*9.81*50\\E_{pot}= 12262.5[J]](https://tex.z-dn.net/?f=E_%7Bpot%7D%3D25%2A9.81%2A50%5C%5CE_%7Bpot%7D%3D%2012262.5%5BJ%5D)
When the rock falls the potential energy is converted into kinetic energy.

where:
Ek = kinetic energy [J]
v = velocity [m/s]
Now clearing v:
![v^{2} =\frac{E_{k}*2}{m}\\v=\sqrt{(2*12262)/25}\\v = 31.32 [m/s]](https://tex.z-dn.net/?f=v%5E%7B2%7D%20%3D%5Cfrac%7BE_%7Bk%7D%2A2%7D%7Bm%7D%5C%5Cv%3D%5Csqrt%7B%282%2A12262%29%2F25%7D%5C%5Cv%20%3D%2031.32%20%5Bm%2Fs%5D)
Answer:
The formula for the calculation of the magnetic field inside a solenoid is
B = μo*n*I
where
μo: vacuum permeability
n: turns per meter
I: current
The magnetic field inside de solenoid is constant. In the case of a small-radius solenoid inside a large-radius solenoid, the magnetic field inside the small-radius solenoid is the magnetic field generated by itself plus the magnetic field generated by the large-radius solenoid. (The radius of the solenoids does not have to be with the instensity of the magnetic field):
BT = Bs + Bl
Bs: magnetic fiel of the small-radius solenoid
Bl: magnetic fiel of the large-radius solenoid
Hence:
BT = 2*μo*n*I