Q: An object acted on by three forces moves with constant velocity. One force acting on the object is in the positive x direction and has a magnitude of 6.3 N; a second force has a magnitude of 5.1 N and points in the negative y direction. Find the direction and magnitude of the third force acting on the object.
A: The third force neutralizes the first two, for a net force of 0N. force=mass x acceleration Because it has a constant velocity, acceleration, and therefore force, are equal to 0. To find the neutralizing force you must find resultant of the first 2 vector forces: One is 6.3 in the +x direction (or 0 degrees) and one is 5.1 in the -y (270 degrees). Therefore the x of the resultant is 6.3, y of resultant is = - 5.1. You need to find the angle, which is always the inverse tangent of y/x Inverse tan(-5.1/6.3) = -39 degrees You now need to find the magnitude of the resultant vector, using pythagorean theorem. 6.3^2 + (-5.1)^2 = C^2 Solve for C. C = 8.1 So the resultant of the 2 forces is 8.1N @ -39 degrees. You need an opposite and equal force, so you add 180 degrees and get: 8.1N @ 141 degrees. (To be frank the person above me doesn't know what they are talking about *rolleyes*)