My educated guess would be that i'm wrong(adsbygoogle = window.adsbygoogle || []).push({});

1. The problem statement, all variables and given/known data

A factory worker pushes a 30kg crate a distance of 4,5m along a floor at constant velocity, the coefficient of kinetic friction between the crate and floor is 0.25

The angle he pushes the crate with is 30 degrees below the horizontal

2. Relevant equations

Work = F * s * cos(angle)

Normal force = mg

3. The attempt at a solution

What i do know is that since the velocity is constant, the total work done on the crate is 0

So Work total =Wt = Work done by worker + Work done on crate by friction = 0

So Work done by worker = - work done on crate by friction

Work done by worker = F*s * cos(30)

work done by friction = F*s * cos(180) = F*s*-1

I find the friction force by using the frictional coefficient * the normal force

So F = 0.25 * 30 * 9.81 = 73,575N

F*s*cos(30)= -73,575N*s*-1

I can remove s from both sides

F*cos(30) = 73,575N

F=73,575/cos30 = 84,95N

Which is the wrong result

The book states that the answer is 99.2N

What am i doing wrong ?

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

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# Homework Help: Who is right - me or the book - work and kinetic energy

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