How much force is needed to cause a car weighing 800kg to accelerate at a rate of 5 m/s^2? Suppose after accelerating the car begins to travel at a constant velocity of 10 m/s. How much momentum has the car generated at the constant velocity? Use a few short sentences to describe how you arrived at your answer.

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".