An object of mass 4 kg is sliding with a constant velocity of 4 m/s on a frictionless horizontal table. The net external force required to keep the object moving with the same constant velocity is:

The magnitude and direction of the acceleration produced in a body of mass 5 kg when two mutually perpendicular forces 8 N and 6 N act on it, are respectively:

Two blocks of masses 3 kg and 1 kg are placed in contact on a smooth horizontal surface. A horizontal force F = 5 N is applied on the 3 kg block from the left. Find the contact force exerted between the two bodies.