How much power must you exert to horizontally drag a 25.0 kg table 10 m across a brick floor in 30 s.

Question

How much power must you exert to horizontally drag a 25.0 kg table 10 m across a brick floor in 30 s at a constant velocity, assuming the coefficient of kinetic friction between the table and floor is 0.550?

Answer 1

Power = (Friction Force) * (Velocity)

Power = (muk * Normal Force) * (Velocity)

Power = (muk * weight) * (Velocity)

Power = (muk * mass * gravity) * (Displacement / Time)

Power = (0.550 * 25.0 * 9.81) * (10 /30)

Power ~= 44.96 Watts

Answer 2

Force to pull the block:

F = (25kg)(0.55) = 13.75kg force * 9.8m/s/s = 134.75 newtons

Work done on block

W = F * D = 134.75 * 25 = 3368.75 Newton meters

EDIT:

Should be W = F * D = 134.75 * 10 = 1347.5 Newton meters

Power

P = W/T = (3368.75 Nm)/(30s) = 112.3 Nm/s or watts

EDIT:

Should be  P = W/T = (1347.5 Nm)/(30s) = 44.9 Nm/s or watts

Woops! Bekki you are correct. Next time I'll wait to plug and chug.

Answer 3

Draw your force diagram with four forces--weight, normal force, friction, and the pulling force you exert.  All the forces must add to zero to have a constant velocity.

The weight of the table is mg (down)

So the normal force equals the weight (up).

The force of friction is the normal force times the coefficient of kinetic friction.  This is equal to the force you must exert.

F = mu m g

The power is equal to the force times the velocity

P = Fv

= (mu m g) (d / t)

They give you the coefficient of friction, mu, the mass, m, the distance, d, and the time, t.  You know the gravitational acceleration, g.  Grab a calculator.

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The answer below (Eng) is correct, but Mike's is off--he plugged in the mass where he should have put in distance.  This is the result of a fundamental error in his problem solving technique.  If they ask you for power, solve for the power using symbols and THEN plug in the numbers.  Don't plug in numbers to find the force and the work.  They don't ask for it.  It gives you more chances to make a mistake.  It makes your work difficult to grade (I don't give partial credit once numbers go in).  And it obscures the physics content of your final answer--which variables contribute and how.