A 4 kg object, moving on a flat horizontal surface in a straight line, experiences a net force, F = -2t. If the initial velocity is +4 m/s, at what time will the object come to rest?

Which of the following situations is impossible? a) an object has velocity directed east and acceleration directed east. b) an object has zero velocity but non-zero acceleration. c) an object has constant non-zero velocity and changing acceleration. d) an object has velocity directed east and acceleration directed west. e) an object has constant non-zero acceleration and changing velocity.