The answer is D. Isotopes.
Hope that helped.
For the second question you’re solving for resistance. resistance= voltage/ current. 120/0.5= 240. the answer is 240 ohms
for the third question you would do 2*4 since it’s asking for voltage, the answer is 8 volts :)
Complete Question
A small metal sphere, carrying a net charge q1=−2μC, is held in a stationary position by insulating supports. A second small metal sphere, with a net charge of q2= -8μC and mass 1.50g, is projected toward q1. When the two spheres are 0.80m apart, q2 is moving toward q1 with speed 20ms−1. Assume that the two spheres can be treated as point charges. You can ignore the force of gravity.The speed of q2 when the spheres are 0.400m apart is.
Answer:
The value 
Explanation:
From the question we are told that
The charge on the first sphere is 
The charge on the second sphere is 
The mass of the second charge is 
The distance apart is 
The speed of the second sphere is 
Generally the total energy possessed by when
and
are separated by
is mathematically represented

Here KE is the kinetic energy which is mathematically represented as

substituting value


And U is the potential energy which is mathematically represented as

substituting values


So


Generally the total energy possessed by when
and
are separated by
is mathematically represented

Here
is the kinetic energy which is mathematically represented as

substituting value


And
is the potential energy which is mathematically represented as

substituting values


From the law of energy conservation

So


Answer:
d. equal to one-fourth the acceleration at the surface of the asteroid.
Explanation:
The explanation is attached as a picture with this answer
Newton's law of universal gravitation is being used to compare the accelerations at the surface and at the top of the ball's path.
as it can be seen in the explanation that the proportional form of the equation is used because we do not need to necessarily use to final form with "G" for comparison calculations.
As per the given scenario only difference between the two points in the gravitational field is the distance from center of the spherical asteroid, i.e. r.
It is taken 2r for the top is the path. hence we obtain (1/4)g as our answer.
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