AP Physics
posted by J .
While two forces act on it, a particle is to move at the constant velocity v = (3 m/s) i  (4 m/s) j. One of the forces is F1 = (2 N) i + ( 6 N) j. What is the other force?
( _____ N) i + ( _____ N) j
Only two horizontal forces act on a 3.0 kg body that can move over a frictionless floor. One force is 9.0 N, acting due east, and the other is 6.9 N, acting 70° north of west. What is the magnitude of the body's acceleration?

on the first, constant velocity means no net force. So the other force will be the negative of the first.
Second: add the forces
resultantmagnitude=sqrt (9^2+.9^2)