# Homework Help: Inelastic Collision Problem

1. Oct 31, 2007

### Oliviam12

1. The problem statement, all variables and given/known data
A drunk driver strikes a parked car. During the collision the cars become entangled and slide to a stop together. The drunk driver's car has a total mass of 742 kg, and the parked car has a total mass of 776 kg. If the cars slide 18 m before coming to rest, how fast was the drunk driver going? The coefficient of sliding friction between the tires and the road is 0.59.

2. Relevant equations
Err?

3. The attempt at a solution
Not any idea really? Just that I think its inelastic... and that I cant use the equation v1`=m1-m2/m1+m2 V1 to get the answer... How do I incorporate the friction?

2. Oct 31, 2007

### Staff: Mentor

Yes, it's a completely inelastic collision. (What's conserved during the collision?) Treat the problem in two parts: (1) the collision (What's the speed of the two cars immediately after the collision?) (2) the slowing down due to friction.

Work backwards from the given information.

3. Oct 31, 2007

### Oliviam12

Energy is conserved, but I don't know how to find the speed of the two cars after the collision :/

4. Oct 31, 2007

### Staff: Mentor

Energy is not conserved (that's what inelastic means). Work backwards. Hint: What's the force of friction that slows the cars? The acceleration? The speed just after the collision?

5. Oct 31, 2007

### Oliviam12

I am sorry but, I don't understand this problem at all... Can you redirect me to an example problem or a tutorial?

6. Nov 1, 2007

### saket

Go through your text. You should find there that during inelastic collision, only thing that remains conserved is linear momentum. (Here, we are not concerned with rotaion and all.)
So assume initial speed to be 'v' and conserve momentum, to get speed of the two cars, just after the collision. (Note, after collision the two cars stick -- entangle -- to each other.) After obtaining this speed, you can apply work-energy theorem to know the work done by the friction. And, assuming uniform friction, you can get the distance required to stop the cars. Equate it with the given data (18m) to get initial speed 'v'.