What is the acceleration of an object with a 4500g mass when there is a net force o 18 N on it

When the force changes, acceleration changes too, but the magnitude of its change depends on the mass of an object. This is not true in a situation when the mass also changes, e.g., in rocket thrust, where burnt propellants exit from the rocket's nozzle.

Explanation:

the answer is 46 mls because when you add the speed per second it increses the speed