A toy car is placed on a ramp for an experiment. While it is on the ramp, gravity acts as an unbalanced force and causes the car to roll down the ramp. Which of
the following graphs illustrates the car's speed as a function of time while it is
on the ramp?
pesas
Speed
a.
Time
Time
Speed
Speed

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".