Answer:
A)
B) 
Explanation:
Using the free body diagram and according to Newton's first law, we have:

A) Solving (1) for T:

B) Solving (2) for F:

Answer:
mv
Explanation:
momentum = mass * velocity
The answer is D. Sound insulators prevent sound from being transmitted better than elastic solids because sound insulators basically muffle and block the sound waves.
The electron is accelerated through a potential difference of

, so the kinetic energy gained by the electron is equal to its variation of electrical potential energy:

where
m is the electron mass
v is the final speed of the electron
e is the electron charge

is the potential difference
Re-arranging this equation, we can find the speed of the electron before entering the magnetic field:

Now the electron enters the magnetic field. The Lorentz force provides the centripetal force that keeps the electron in circular orbit:

where B is the intensity of the magnetic field and r is the orbital radius. Since the radius is r=25 cm=0.25 m, we can re-arrange this equation to find B: