- #1

## Homework Statement

A car with a mass of 1400 kg is westbound at 50 km/h. It collides at an intersection with a northbound truck having a mass of 2000 kg and traveling at 40 km/h. What is the initial common velocity of the car and trucks after collision if it's an inelastic collision?

## Homework Equations

p = mv

## The Attempt at a Solution

So I got this question wrong, but I can't seem to get the right answer no matter how I look at it. I think maybe I lost marks because I didn't use the method the teacher wanted (which is fine with me)?? Let me know guys.

m

_{1}v

_{1}+ m

_{2}v

_{2}= (m

_{1}+ m

_{2})v

_{f}

(1400kg)(13.888m/s) + 0 = (1400kg + 2000kg)(v

_{fx})

vf = 5.7189... m/s

0 + (2000 kg)(12.5 m/s) = (1400kg + 2000kg)(v

_{fy})

vf = 7.35294.. m/s

(5.7)

^{2}+ (7.3)

^{2}= r

^{2}

vf = 9.3 m/s

tan-1(7.3 / 5.7 m/s)

= 52 N of W

= 128 degrees

I tried a different approach and found P(car) and P(truck), then P(combined), solved for Vf, but I got the same answer:

(1400 kg)(13.888 m/s) = 19443.2 kg m/s West

(2000 kg)(12.5 m/s) = 25000 kg m/s North

pythagorean theorem...

= 31670.77559 kg m/s

momentum is conserved so

31670.78 = (2000 + 1400) vf

vf = 9.3 m/s!