The purpose of the air filter is to

The purpose of the air filter is to remove dust particles, chemicals or biological hazards from the air. Air filters are used extensively in vehicles, personal protection, gas turbines, laboratories, pneumatics and air conditioning systems in buildings such as homes and hospitals, as well as in indoor air purification. The filter element of the air filter may be, for example, activated carbon, paper, fiberglass, cotton, foam or the method may be electric.

the answer is neither ball has a charge.

because if they were both positively charged, they will repel each other.

if they were positively and negatively charged, they will seek.

truck y has a greater velocity than truck x.