# Homework Help: ﬁnd the magnitude and direction of the ﬁnal velocity

1. Jun 9, 2009

### bigboss

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

Two vehicles approach a right angle intersection and then collide. After the collision, they become entangled. If their mass ratios were 1:4 and their respective speeds as they approached were both 13 m/s, ﬁnd the magnitude and direction of the ﬁnal velocity of the wreck.

A)16.3 m/s at 79° B)13.1 m/s at 79° C)15.7 m/s at 79° D)12.5 m/s at 79°

2. Relevant equations
p=mv. m1v1+m2v2=(m1+m2)vf

3. The attempt at a solution

i found both x and y compontents of the cars, with one car having a mass of 1 kg and another having a mass of 4kg. I ended up getting, 10.7m/s and 76 degrees, but that is not even a choice

2. Jun 9, 2009

### CompuChip

Re: Momentum

Sounds like you're on the right track. Possibly you have just made a little calculation error somewhere. Can you show us what you did?

3. Jun 9, 2009

### bigboss

Re: Momentum

since it is a right angle, one car is going 13 m/s right, while the other is going 13m/s up

so there is a 1:4 ratio of mass

x component) m1v1+m2v2=(m1+m2)v

1(13)+(4*0)=(1+4)V
13/5= vx
vx=2.6 m/s

y component) m1v1+m2v2=(m1+m2)v

(1*0)+(4*13)=(1+4)v
52/5=vy
vy=10.4 m/s

sqrt 10.4^2+2.6^2
= 10.7 m/s
inverse tan of 10.4/2.6= 76 degrees

4. Jun 11, 2009

### CompuChip

Re: Momentum

Frankly, I do not see the error.
I did the calculation myself and I found the same answer.

Perhaps you should go see your teacher and ask him what is wrong with your answer because you absolutely don't see it and have checked it multiple times (that's a polite way of asking if he's sure he isn't wrong )