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

Rain is falling vertically into an open railroad cart which moves along a track at a constant speed. The engine must exert extra force on the cart as it collects water (the water is initially stationary be brought up to the speed of the train).

Calculate this force if v = 20m/s

Water collects at rate of 6kg per minute (=0.1kg/s)

2. Relevant equations

This is where I'm a little confused. I missed this lecture and my online notes confuse me. It says that Newton's 2nd Law can be re-written because, at a constant mass, [tex]\Delta[/tex](mv) = m *[tex]\Delta[/tex]v. Based on this: F = [tex]\Delta[/tex](mv) if the mass is not constant. Is that right?

3. The attempt at a solution

If it's [tex]\Delta[/tex](mv) then won't the answer always be zero since V isn't changing...or am I just making a stupid mistake? Should it be:

(0.2kg/s*20m/s)-(0.1kg/s*20m/s) = 2N?

I appreciate any help I can get on this as I (clearly) don't fully understand it.

Thanks,

Graeme

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# Homework Help: Relationship between Newton's 2nd and Momentum?

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