Calculating Minimum Horsepower for Moving a Mass at a Given Speed

[RileyAllen]

Homework Statement

What minimum horsepower must a motor have to be able to drag a 270 kg box along a level floor at a speed of 1.20 m/s if the coefficient of friction is 0.50?

Homework Equations

Ffr=mu*mg
W=Ffr*d

The Attempt at a Solution

I ended up having W=Fr*d=mu*m*g*d
(.5)*(270)*(1.2)*(1.2)=194.4 J/s=.26 hp

That is way too low.

Can anyone give me any guidance?

 

[Delphi51]

It looks like you just used 1.2 instead of 9.81 in your calc, but it would be better to use P = F*v.
If you don't know this formula, it is from P = W/t = F*d/t = F*v.

 

[RileyAllen]

Is the way I tried it wrong? I ended up with hp=2.13 and that still seems pretty low

 

[Delphi51]

That answer looks good!
Why does it seem low? Picture a pair of horses pulling a sled with a big guy on it at 5 km/hr?