In an inertial frame of reference, a series of experiments is conducted. In each experiment, two or three forces are applied to an object. The magnitudes of these forces are given. No other forces are acting on the object. In which cases may the object possibly move at a constant velocity of 256m/s?

(1) 2 N; 2 N
(2) 200 N; 200 N
(3) 200 N; 201 N
(4) 2 N; 2 N; 4 N
(5) 2 N; 2 N; 2 N
(6) 2 N; 2 N; 3 N
(7) 2 N; 2 N; 5 N
(8) 200 N; 200 N; 5 N

For the body to move with a constant velocity the acceleration must be zero. Because, acceleration is the rate of change of velocity. And for zero acceleration, the net unbalanced force must also be equal to zero. According to Newton's Second Law:

F = ma = m(0) = 0

Therefore, object can move with constant velocity of 256 m/s, in those cases, for which the vector sum of the forces can somehow become zero.

Those cases are mentioned below, with the expression for zero net force:

(1) 2 N; 2 N : F = 2 N - 2 N = 0 N

(2) 200 N; 200 N : F = 200 N - 200 N = 0 N

(4) 2 N; 2 N; 4 N : F = 2 N + 2 N - 4 N = 0 N (OR) F = 4 N - 2 N - 2 N = 0 N