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

The crate has a mass of 80 kg and is being towed by a chain which is always directed at 20º from the horizontal has shown. Determine the crate's acceleration int= 2 s if the coefficient of static friction isμ_{s}= 0.4, the coefficient of kinetic friction isμ_{k}= 0.3, and the towing force isP= (90t^{2}) N, wheretis in seconds.

2. Relevant equations

ΣF=ma

3. The attempt at a solution

ΣF_{x}=ma_{x}

Pcos(20º) -μ_{k}mg =ma

84.57t^{2}- 235.44 = (80 kg)a

solving forawhent= 2

a= 1.29 m/s^{2}

The answer at the back of my book isa= 1.75 m/s^{2}. I think I'm supposed to consider that static friction force is greater than kinetic friction force, but I can't figure out how to do that.

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# Homework Help: Kinetics, force and acceleration

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