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Entr0py

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## Homework Statement

A 2000-lb car traveling north at 60 mph collides with a 5000-lb car traveling east at 40 mph. The cars stick together after the collision. Find the velocity (magnitude and direction) of the cars just after the collision.

## Homework Equations

conservation of linear momentum

## The Attempt at a Solution

Firstly, I need to find the masses of each car. Car 1 has weight of 2000 lbs and has a mass of (2000/32.2) about 62 slugs. Car 2 has weight of 5000 lbs and has mass of (5000/32.2) about 155 slugs. That said, the initial momentum of car 1 equals m(1) times v(1) or (62 slugs times 60 mph) = 3720 slug-m/h. Initial momentum of car 2 equals m(2) times v(2) or (155 times 40 mph) = 6200 slug-m/h. So the total initial momentum is 9920 slug-m/h.

The final momentum of the cars= (total mass of cars since they stick together) times (new velocity) which equals 217v, so v= 9920/217 or 45.7 mph. To find the direction of velocity after collision, wouldn't I do arctan(40/60) = 33.7 degrees NE.

Now I must be doing something wrong because in the back of the book, the answer is 33.3 mph at 31 degrees NE. So i can't figure out what I'm doing wrong.