Concept #1: Static Friction & Equilibrium

Practice: The system below does not move. Find the minimum value that μ,S (between 8 kg block and table) can have.

Practice: A 15 kg block is initially at rest on a horizontal surface. The coefficients of friction between the block and the surface are 0.5 and 0.7. How hard must you push down the block to keep a 300 N force in the +x from moving it?

Consider the figure below, graphing the force applied on a 200 kg box vs time. During the first 0.5 s on the graph, the box remains at rest, while during the remaining time on the graph, the box moves at a constant speed of 15 m/s. What is the maximum coefficient of kinetic friction during the motion of the box?

Consider the figure below, graphing the force applied on a 200 kg box vs time. During the first 0.5 s on the graph, the box remains at rest, while during the remaining time on the graph, the box moves at a constant speed of 15 m/s. Assume that the decrease in the coefficient of kinetic friction is due to changes in the surface the box moves across. How far across this surface does the box have to travel for the coefficient of kinetic friction to reach half its maximum value?

A 5 kg box sits atop a 20 kg box inside an elevator. If the elevator was accelerating upwards at 2 m/s2, how much force would you have to push the 20 kg box so that the 5 kg box falls off? Assume that there is no friction between the 20 kg box and the floor, and μs = 0.4 between the 5 kg and 10 kg box.

Consider the figure below, graphing the force applied on a 200 kg box vs time. During the first 0.5 s on the graph, the box remains at rest, while during the remaining time on the graph, the box moves at a constant speed of 15 m/s. What is the coefficient of static friction?

Consider the figure below, graphing the force applied on a 200 kg box vs time. During the first 0.5 s on the graph, the box remains at rest, while during the remaining time on the graph, the box moves at a constant speed of 15 m/s. At what time would the force of static friction be 0.5 kN?