(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

I'm working on a similar problem and someone else solved the problem (along with the steps). I looked at what they did but I'm really confused on 2 of the steps.

Here is the problem:

In a 30-s interval, 500 hailstones strike a glass window of area 0.60 m2 at an angle of 45o to the window surface. Each hailstone has a mass of 5.0 g (0.005 kg) and a speed of 8.0 m/s. If the collisions are elastic, find the average force.

3. The attempt at a solution

vx = v cos 45o (Why is it not sin 45?)

vx = (8.0 m/s)(0.707) = 5.66 m/s

px = m vx = (0.005 kg)(5.66 m/s) = 2.83 x 10 - 2 kg-m/s

I understand everything up to this next step. What I don't understand is why is the momentum in the x direction multipied by two?

px = 2 px = 5.66 x 10 - 2 kg-m/s

F = pxtot/t

F = (500)(5.66 x 10 - 2 kg-m/s)/30 s

F = 0.943 kg-m/s2

F = 0.943 N

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# Hailstones and Momentum

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