Forces

An object is placed on a frictionless incline at 30°. With g = 10 m/s², what is its acceleration down the incline?

A car rounds a flat curve of radius 50 m. The coefficient of friction between tires and road is 0.4, g = 10 m/s². What is the maximum speed without skidding?

A simple bridge is made of five thin rods rigidly connected at four vertices (see figure). The ground is frictionless, so that it can only exert vertical normal forces at B and D. The weight of the bridge is negligible, but a person stands at its middle, exerting a downward force F at vertex C. In static equilibrium, each rod can be experiencing either tension or compression. Which of the following is true?