Question

# In this example we will calculate the coefficients of static and kinetic friction using two equations...

In this example we will calculate the coefficients of static and kinetic friction using two equations along with Newton’s second law of motion. Suppose that a delivery company has just unloaded a 500 N crate full of home exercise equipment in your level driveway. You find that to get it started moving toward your garage, you have to pull with a horizontal force of magnitude 230 N. Once the crate “breaks loose” and starts to move, you can keep it moving at constant velocity with only 200 N of force. What are the coefficients of static and kinetic friction?

1. Suppose you wet down your driveway prior to delivery, so that μs=0.30 and μk=0.25. What horizontal force is required to start the crate moving? Express your answer in newtons to three significant figures.

2. What force is required to keep it sliding at constant velocity? Express your answer in newtons to three significant figures.