# Homework Help: Principle of Conservation of Linear Momentum

1. Mar 22, 2006

### helen3743

I also need help how to start his problem:

"By accident, a large plate is dropped and breaks into three pieces. The pieces fly apart parallel to the floor, with v1 = 3.10 m/s and v2 = 1.60 m/s. As the plate falls, its momentum has only a vertical component, and no component parallel to the floor. After the collision, the component of the total momentum parallel to the floor must remain zero, since the net external force acting on the plate has no component parallel to the floor. Using the data shown in the drawing, find the masses of pieces 1 and 2."

In the drawing, it shows m1 & m2 falling at an angle to the floor but m3 has no angle, and just has a velocity of 3.07 m/s pointing down with a mass of 1.3kg.

How would the formula look like to solve this problem?
I know the normal formula looks like:
x comp & y comp:
m1vf1 + m2vf2 =m1vo1 + m2vo2

I know how to find velocities incorporation the angles, (like doing m1sin25)but I don't know where to fit in the third mass in the formula.

Do you? Thanks!

2. Mar 22, 2006

### Chi Meson

You have two unknowns, m1 and m2.

That means you need two equations. Balance the x-momenta for one equation, and balance the y-momenta for the other.