How Is the Average Pressure of Hailstones on a Window Calculated?

[xago]

Homework Statement

During a hailstorm, hailstones with an average mass of 2g and a speed of 15m/s fall vertically down and strike a winshield angled at 45 degrees and bounce off at the same speed horizontally. The area of the window is .5m² What is the average pressure they exert on the window?

Homework Equations

The Attempt at a Solution

So far this is what I've worked out:
Pressure = Force/Area
Force = ma but since there is no loss in velocity then that means that a=0 and the stones exert no force on the window?

 

[Redbelly98]

Can you relate force to the change in momentum?