1. A car goes from 6 m/s at time 5 s to 8 m/s at time 10 s. Is the car's acceleration constant? 2. A book is pushed with a horizontal force of 30 N on a horizontal table and moves with constant velocity. What is the magnitude of the friction force between the book and the table? 3. A box slides down a vertical wall. What is the normal force on the box due to the wall? Explain your answer.