A sled weighing 60 N rests on a ramp at 20 degrees.?

Question

Between the sled and the plane the coefficient of static friction is 0.26, and the coefficient of kinetic friction is 0.19. What is the minimum magnitude of the force F, parallel to the plane, athat will prevent the sled from slipping down teh plane? what si the minimum magnitude F taht will start teh sled mobing up the plaen? What value of F is requuired to move the block up the plane at constant velocity?

Answer 1

1. Resolve the sled's weight into components perpendicular to the plane and parallel to the plane: 60 N cos 20 deg and 60 N sin 20 deg, respectively.

2. Figure the "force" of static and kinetic friction: the perpendicular force times the respective coefficients of friction.

To prevent the sled from sliding down the plane, the force applied, plus the "force" of static friction (from paragraph 2) must equal (at least) the component parallel to the plane (from paragraph 1).

To start the sled moving up the plane, the force applied, MINUS the "force" of static friction must equal (at least) the component parallel to the plane.

To move the block up the plane at a constant velocity, the force applied, MINUS the "force" of KINETIC friction must equal (EXACTLY) the component parallel to the plane.