If a diagonal line going down to up means a increase of acceleration what does a lie going up to down mean?

Truck traveling west on the highway experiences an acceleration to the east. what could be the cause of this acceleration

Can anybody me with this? ? (picture included.)

The electric field direction is defined by the direction of the force felt by (select one of the following answers): 1. a negative charge. 2. a positive charge. 3. both positive and negative charges.