If the same net force is applied to a 7 kg object and a 21 kg object, then the 21 kg object accelerates three times faster than the 7 kg object. the 7 kg object accelerates three times faster than the 21 kg object. both objects accelerate at the same rate because the force is the same neither object will accelerate because there is a net force on the objects. what is the acceleration due to gravity on mars?

Force = (mass) x (acceleration)

Acceleration = (force) / (mass)  ==> 
                                                         This says that with the same force,
acceleration is inversely proportional to mass.  That means that with the
same force, greater mass has smaller acceleration.  You know that, because
when you push on a pencil and a school bus with equal force, the pencil has
greater acceleration.

The acceleration of the 7kg object is three times the acceleration
of the 21kg object.

The acceleration of gravity on Mars is 3.711 m/s².