Answer:
A.The positive z-direction
Explanation:
We are given that
Linear charge density of long line which is located on the x-axis=
Linear charge density of another long line which is located on the y-axis=
We have to find the direction of electric field at z=a on the positive z-axis if
and
are positive.
The direction of electric field at z=a on the positive z-axis is positive z-direction .
Because
and
are positive and the electric field is applied away from the positive charge.
Hence, option A is true.
A.The positive z-direction
Explanation:
Mass of bumper cars, 
Initial speed of car A, 
Initial speed of car Z, 
Final speed of car A after the collision, 
We need to find the velocity of car Z after the collision. Let it is equal to
. Using the conservation of momentum as :




So, the velocity of car Z after the collision is (-12 m/s). Hence, this is the required solution.
Every person is different. But for a planet-wide overall average that roughly represents all human beings on Earth, the figures usually used are:
from 20 Hz to 20,000 Hz .