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Raindrops keep falling on your head at a rate of 4 drops per second. The raindrops each have a mass of 1.6 x 10^-6 kg and fall with a velocity of 25 m/s. Assuming that on making contact the drops come to a rest and do not rebound, calculate the perceived force each second.

There are two approaches and I don't know why one is more correct than the other. The first is the solution I was given in the text. The second is another solution.

1st:

a=Δv/Δt=0-25/1=25 m/s^2.

F(one drop)=ma=1.6x10^-6*-25m/s^2=4x10^-5 N.

F(4 drops)=4*F(one drop)=1.6x10^-4 N.<-------------

(along with considerations for negative signs, not shown)

2nd:

Since there are 4 drops per second, there is .25 seconds per drop.

a=Δv/Δt=25/.25=100m/s^2.

F(one drop)=1.6x10^-6*100m/s^2=1.6x10^-6 N.

F(4 drops)=4*F(one drop)=6.4x10^-4 N.<---------------

(again with directional considerations not shown)

Is this simply a poorly worded problem, or is there some subtlety I'm missing? Thanks.

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# Homework Help: Raindrops problem

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