Answer:
y = 10.2 m
Explanation:
It is given that,
Charge, 
It is placed at a distance of 9 cm at x axis
Charge, 
It is placed at a distance of 16 cm at x axis
We need to find the point on the y-axis where the electric potential zero. The net potential on y-axis is equal to 0. So,

Here,

So,

Squaring both sides,

So, at a distance of 10.2 m on the y axis the electric potential equals 0.
Do u know Chinese ?if yes I can explain to u easily
Its actually C. I did the question on USA test prep and it said the correct answer was C.
Answer:
7.9m/s
Explanation:
We are given that
Mass of wagon=40 kg

Tension=
Initial velocity of wagon=
Displacement=s=80 m
Net force applied on wagon=
By using 

We know that

Using the formula

