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A 1,440-N crate is being pushed across a level floor at a constant speed by a force of 270 N at an angle of 20.0° below the horizontal

(a) What is the coefficient of kinetic friction between the crate and the floor?

I know how to do this. The answer is .165

Heres how I solved it..

270sin20 = 92 N

270cos20 = 254 N

1440N + 92N = 1532N

Ff=uk(n)

254N=uk(1532)

uk= .165

The only thing I don't quite get is why do I use 254N, the product of 270cos20, as the Ff and why is 1532N the normal force?

Thanks.