- #1

Hemmelig

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## Homework Statement

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

## Homework Equations

Work = F * s * cos(angle)

Normal force = mg

## 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 ?