In the test of verifying Newton's second law, why do we sometimes make the weight mass m far less than the trolley mass m? Sometimes we don't need to?

In the test of verifying Newton's second law, why do we sometimes make the weight mass m far less than the trolley mass m? Sometimes we don't need to?

If the object of study is the car and the weight as a whole, then do not "m is far less than the car mass m" condition; if the object of study is the car, then "m is far less than the car mass m" condition

Two identical objects move in a straight line at a constant speed on the same horizontal plane, if the air resistance is not considered, and v1f2
c．F1

A
Because when moving at a constant speed, the object is in equilibrium, and the pulling force is equal to the friction force. Because it is the same object and plane, the friction force must be the same. F = UMG, so the pulling force is the same