This problem examines coordinates and equations of motion, including the direction of velocity and multiple solutions.

(1) according to the meaning of the question, there are

X(p)=20-5t

X(q)=-4t

x(n)=-40+8t(t & lt； =5); x(n)=-8t+40(t & gt； 5)

(2) When n and q overlap for the first time:

-40+8t=-4t, so t= 10/3.

At this time, x (p) = 20-5 *10/3 =10/3.

The moment when n and q first overlap is:

-8t+40=-4t, so t= 10,

At this time, X(p)=20-5* 10=-30.

(3)

When t & lt=5, there is

-4t-(-40+8t)=20-5t-(-4t), and t = 20/1.

When t >; At 5 o'clock, yes

-8t+40-(-4t)=20-5t-(-4t), and t=20/3 is obtained.

Hope to adopt! !