Explanation:
(a) Formula to calculate the density is as follows.

= 
= 
Now, calculate the charge as follows.

= 
=
C
or, = 101.06 nC
(b) For r = 6.50 cm, the value of charge will be calculated as follows.

= 
= 7.454 
Compressional waves can travel through all states of matter.
Answer:
This is known as a Galilean transformation where
V' = V - U
Where the primed frame is the Earth frame and the unprimed frame is the frame moving with respect to the moving frame
V - speed of object in the unprimed frame
U - speed of primed frame with respect to the unprimed frame
Here we have:
V = -15 m/s speed of ball in the moving frame (the truck)
U = -20 m/s speed of primed (rest) frame with respect to moving frame
So V' = -15 - (-20) = 5 m/s
It may help if you draw a vector representing the moving frame and then add
a vector representing the speed of the ball in the moving frame.
<span>In a 2-dimensional coordinate system, the x- and y-axes
are typically perpendicular to each other. (C) </span>