D, all notebooks would hit the floor at the same time. The time it takes to hit the floor is independent of their weight, but rather dependent on the acceleration of gravity. Since gravity is constant, they will all hit the floor at the same time.
We can apply the law of conservation of energy here. The total energy of the proton must remain constant, so the sum of the variation of electric potential energy and of kinetic energy of the proton must be zero:

which means

The variation of electric potential energy is equal to the product between the charge of the proton (q=1eV) and the potential difference (

):

Therefore, the kinetic energy gained by the proton is

<span>And since the initial kinetic energy of the proton was zero (it started from rest), then this 1000 eV corresponds to the final kinetic energy of the proton.</span>
1) First of all, let's find the resistance of the wire by using Ohm's law:

where V is the potential difference applied on the wire, I the current and R the resistance. For the resistor in the problem we have:

2) Now that we have the value of the resistance, we can find the resistivity of the wire

by using the following relationship:

Where A is the cross-sectional area of the wire and L its length.
We already have its length

, while we need to calculate the area A starting from the radius:

And now we can find the resistivity:
The Equivalent resistance is :

The solution is in attachment for solution ~