A chair of mass 15.0 kg is sitting on the horizontal floor; the floor is not frictionless. You push on the chair with a force F = 39.0 N that is directed at an angle of 35.0∘ below the horizontal and the chair slides along the floor.   Use Newton's laws to calculate the normal force that the floor exerts on the chair.

One block rests upon a horizontal surface. A second identical block rests upon the first one. The coefficient of static friction between the blocks is the same as the coefficient of static friction between the lower block and the horizontal surface. A horizontal force is applied to the upper block, and its magnitude is slowly increased. When the force reaches 49.3 N, the upper block just begins to slide. The force is then removed from the upper block, and the blocks are returned to their original configuration. What is the magnitude of the horizontal force that should be applied to the lower block, so that it just begins to slide out from under the upper block?

A girl is sledding down a slope that is inclined at 30.0° with respect to the horizontal. The wind is aiding the motion by providing a steady force of 183. N that is parallel to the motion of the sled. The combined mass of the girl and the sled is 73.5 kg, and the coefficient of kinetic friction between the snow and the runners of the sled is 0.163. How much time is required for the sled to travel down a 110-m slope, starting from rest?

A 20 kg box is resting on horizontal surface initially. Then a F = 50 N force pulls on the box by a cord at an angle of 20 degrees above horizontal. The kinetic frictional coefficient is 0.20.