Question

an object was accelerated with a force of 150 N from rest to a velocity of 10m/s in 5 sec. the force of friction opposing the object was 100N. What was the object's mass

Answer 1

Force = (mass) x (acceleration)

Mass  =  (force) / (acceleration)

There was 150N of force in one direction and 100N of 'force' in
the other direction.  The net force on  the object was (150 - 100) = 50N .

Acceleration = (change in speed) / (time for the change)
                     = (10 m/s) / (5s)  =  2 m/s²

Mass = (net force) / (acceleration) = (50 N) / (2 m/s²) = 25 kilograms