# Homework Help: Air Track Problem with friction

1. Oct 26, 2009

### Wishingwell

1. The problem statement, all variables and given/known data

An air-track glider of mass 0.109 kg is attached to the end of a horizontal air track by a spring with force constant 22.5 N/m

(a) With the air track turned off, the glider travels 8.8 cm before it stops instantaneously. How large would the coefficient of static friction μs have to be to keep the glider from springing back to the left?

(b) If the coefficient of static friction between the glider and the track is μs= 0.55, what is the maximum initial speed v1 that the glider can be given and remain at rest after it stops instantaneously? With the air track turned off, the coefficient of kinetic friction is μk= 0.54.

2. Relevant equations
PE = .5kx^2
F = -kx

3. The attempt at a solution

My main problem with this is that I have no idea how to set up the problem when friction is involved. I assumed it was μmg from earlier problems but that was dead wrong. Can anyone help me out?

2. Oct 27, 2009

### kuruman

Reason it out. If the glider travels 8.8 cm, the spring is extended by 8.8 cm. Can you find the force that the spring exerts on the glider? If so, then the maximum force of static friction must be at least that much to prevent the glider from being pulled back.