A horizontal line on a speed/time graph means a constant speed.
Hi i play softball so the answer is the letter:
A or D but i think D
Answer:

Explanation:
Here we know that for the given system of charge we have no loss of energy as there is no friction force on it
So we will have


now we know when particle will reach the closest distance then due to electrostatic repulsion the speed will become zero.
So we have



so distance moved by the particle is given as



This question is poorly stated, but I assume you mean what conditions are needed. It would have to be cold outside, correct?
Answer:
Part a)

part b)

Part c)

Part d)
here since wave is moving in negative direction so the sign of
must be positive
Explanation:
As we know that the speed of wave in string is given by

so we have


now we have


now we have
Part a)
= amplitude of wave

part b)

here we know that


so we have


Part c)

Part d)
here since wave is moving in negative direction so the sign of
must be positive