Section 9.2

Solving Static Problems

Solving Static Problems

• How do I solve static problems?

Solving Statics Problems1. Choose one object at a time, and make a free-body

diagram showing all the forces on it and where they act.

2. Choose a coordinate system and resolve forces into components.

3. Write equilibrium equations for the forces.

4. Choose any axis perpendicular to the plane of the forces and write the torque equilibrium equation. A clever choice here can simplify the problem enormously.

5. Solve.

See Saw

A board of mass M = 2.0 kg serves as a see saw for two children. Find x.

Balancing Forces

A uniform 1500 kg beam, 20.0 m long, supports a 15,000 kg printing press 5.0 m from the right support column. Calculate the force on each of the vertical support columns.

Homework

• Page 247, # 1 - 8

Cantilevers• A beam that extends

beyond its supports

• Diving board

• If you get a – sign on your force, it means it points in the opposite direction

Cantilevers

• How would you set up the torque and force equations?

Homework

• Page 247, # 9 - 15

Example

• If there is a cable or cord, it can only support forces along its length.

• Forces perpendicular to a cable would cause it to bend

ExampleA uniform beam, 2.20 m long with a mass of 25.0 kg, is mounted by a hinge on a wall. The beam is held by a cable with an angle of 30° from the beam. The mass of the sign is 28.0 kg. Find the FT in the cable and the x and y components of FH.

Homework

Page 248, # 18 – 24, skip 21