4. After a disagreement over the names of characters in physics problems, Dhanush and Salena decide to settle their dispute with a friendly race. Both start from rest, but Dhanush distracts Salena so that she ends up leaving the starting line one second after Dhanush. Salena moves with a constant acceleration of 4.5 m/sz, while Dhanush maintains an acceleration of 4.1 m/sz. a) Find the time at which Salena overtakes Dhanush. b) Draw motion diagrams for a car speeding up in the positive direction, slowing down in the positive direction, speeding up in the negative direction, and slowing down in the negative direction. List the signs of the velocity and acceleration for each. c) If a moving object has no acceleration, is that object at rest? Why or why not