A 9 kg object with a speed of 27.0 m/s strikes a steel plate at
an angle of 45.0 degrees with the normal to the plate, and rebounds
at the same speed and angle on the other side of the normal. What
is the change (in magnitude only) of the linear momentum of the
object (in kilogram-meters/second)?
What I am stuck on here is the fact that there is supposedly a change in magnitude of the linear momentum in the first place. The picture below is a bit blurry, but it's to give you an idea of how I'm visualizing the system.
I am approaching this as an isolated system of a ball and plate. When I set up the equation for conservation of linear momentum, p1i+p2i = p1f+p2f the object 2 (steel plate) momentum cancels out on both sides (stationary object) and I'm left with p1i=p1f where p=m1v1i
When I solve that equation, I get 228.022 kg*m/s for both sides, which shows that there is no change in linear momentum. That answer is wrong, so there has to be some kind of condition that I'm not taking into consideration. Please walk me through this and I'll award maximum points.