The doppler effect suggest that sound waves are relative to the observer. you know if an object is coming or going from the sound it makes. light waves follow the doppler effect also. however, instead of sound changing, you know if an object is coming or going

This is for my 8th grade science class, i really don’t understand. can someone me? , lol.

The total amount of energy contained in an object

Aparticle's position is given by x = 3.00 - 9.00t + 3t2, in which x is in meters and t is in seconds. (a) what is its velocity at t = 1 s? (b) is it moving in the positive or negative direction of x just then? (c) what is its speed just then? (d) is the speed increasing or decreasing just then? (try answering the next two questions without further calculation.) (e) is there ever an instant when the velocity is zero? if so, give the time t; if not, answer "0". (f) is there a time after t = 3 s when the particle is moving in the negative direction of x? if so, give the time t; if not, answer "0".