# Physics 12 vector (sin law, cos law) problem

1. Jun 28, 2013

### gdhillon

:An object explodes into three equal masses. One mass moves East at a velocity of 15.0
m/s. If a second mass moves at a velocity of 10.0 m/s 45.0 South of East, what is the
velocity of the third mass?

I drew these vectors tip to tail, then used cos law to determine the velocity vector of the first mass, c^2=a^2+b^2-2abcosC...subing in numbers i got c^2=15^2+10^2-2(15)(10)cos45
c^2=325-300cos45= 10.625. then by using sin law i got the angle. sin45/10=sinc/10.239 giving me 11m/s @49 degrees S of E

2. Jun 29, 2013

### Simon Bridge

Cool - did you have a question?
In order to provide you with advice we need to know what your concern is ... otherwise you are just inviting random comment that may or may not be useful to you. Please post a question.

Notice that there is an implicit assumption in your working that you will need to make explicit if this is a long-answer.

Last edited: Jun 29, 2013
3. Jun 29, 2013

### tim9000

'yeah, what he said'.

Well was the sum zero?

4. Jun 29, 2013

### Simon Bridge

Actually I think just sketching all three vectors on an axis should tell us right away if it's right ...

5. Jun 29, 2013

### tim9000

Yes, I skimmed over the top to tail part, I invisioned them all emminating from a point of origin.