# Homework Help: Collision between two cars

1. Nov 24, 2009

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

The driver of a 3850 lb Pontiac traveling East at 32 miles/hr has a collision with a 3100 lb Toyota traveling East at 24 miles/hr. The coefficient of restitution is .27. Find:
i) The final speed of the Pontiac after the collision
ii) The final speed of the Toyota after the collision

3850lb = 1744kg
3100lb = 1404kg
32 miles/hr = 46.93 ft/s
24 miles/hr = 35.2 ft/s
Cr = .27

2. Relevant equations

I'm attempting to solve i) and ii) using the equation:

3. The attempt at a solution

I need to do the work in ft/s & kg

Appx - 40.26 ft/s for m1'
Appx - 43.45 ft/s for m2'

Does it look right for this type of problem?

iii) The kinetic energy lost in the collision

KE = (1/2)(m)(v2 )

KE (m1) = (1/2)(1744kg)(14.3m/s)2
KE (m1') = (1/2)(1744kg)(12.27m/s)2
KE (m2) = (1/2)(1404kg)(10.73m/s)2
KE (m2') = (1/2)(1404kg)(13.24m/s)2

KE (m1) appx = 178315
KE (m1') appx = 131644
KE (m2) appx = 80823
KE (m2') appx = 123058

(178315+80823) - (131644+123058)

4436 Joules lost :)

iv) Suppose the cars locked together during the collision. Find the final speed of the 2 cars after collision for this case

1744kg*46.93ft/s+1404kg*35.2ft/s
3148kg

= 41.7 ft/s

Last edited: Nov 24, 2009
2. Nov 24, 2009

### Redbelly98

Staff Emeritus
Re: Collisions

Looks good. I haven't checked your arithmetic in detail, but your method looks sound.