(1) A particle move along the x axis, as (SI unit). (a) The functions of its velocity and accelerator vector against time； (10 marks ) (b) Its average velocity in the first 3 seconds. (10 marks )

the moving of the box is a result of centripetal force. think of that  as a car or a truck in this case creates a turn, the force of friction performing upon the turned wheels of the car runs centripetal force obligatory for circular motion for the things inside it.