Third, the friction force, which acts opposite to its direction of motion and is given as. Second, the normal force of the plane, which is given as. First, it's weight under the influence of gravity, which is given as. This block has three forces acting on it. The free body diagram of the block is given above. The only force acting on the 30 kg block is the tension, and the acceleration is what we found above. ĭo this by using Newton's second law again, except for only one of the blocks: Now that we have acceleration, we need to write a new equation in which the tension force does not cancel out so that we can solve for the tension. We can solve for acceleration, since the tensions cancel out. In this problem, the two tension forces form an action/reaction pair and therefore are equal in magnitude but opposite in direction (Newton's third law). Since the blocks are connected by a string, they will therefore accelerate at the same rate, and we can treat them as a system that moves as if it were one object of total mass 80 kg (30 kg plus 50 kg). We are given in the question that the force is 100 N. You could also draw in the force of gravity and the normal force for each block, but they have been omitted from the image because they cancel each other out for each block and because there is no friction in this problem.
Start by drawing in the forces acting on each block.
