ps6a14 - Physics 111.01 October 6, 2008 PS 6a Problem 1 =...

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Physics 111.01 October 6, 2008 PS 6a Problem 1 = Walker 7.38. You raise a bucket of water from the bottom of a deep well. If your power output is 118 W, and the mass of the bucket and the water in it is 4.50 kg, with what speed can you raise the bucket? Ignore the weight of the rope. Solution. We assume that the bucket rises at constant velocity, so that there is no acceleration, and the weight (caused by gravity) is just equal to the force lifting the bucket, equal in magnitude to the tension T . So, there is an upwards force of mg moving at speed v . The power applied is given by PF v == m g v (To see this: work done Fx x FF v tt t power = === ∆∆ ) So, solving for the velocity v , () ( ) 118 N-m/s 2.676 m/s 4.50 kg 9.8 N/kg vm g v P v mg = m g v T g θ m y x y x mg N f mg sin θ mg cos θ d k "" :s i n :c o s Fm a x mg Nm a yN m g θµ θ = −= = Problem 2. (This is nearly identical to a problem you did on HW#5. Now we will do it with the work method.) A 8 kg crate is placed at rest on an incline plane ( s = 1 , k = 0.6 ), whose angle is 60 o . It then slides 5 m down the incline. a.) Find the work done by each force on the crate after sliding this distance: work done by normal force: work done by gravity:

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This note was uploaded on 05/13/2010 for the course PHYSICS 111 taught by Professor Staff during the Fall '08 term at S.F. State.

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ps6a14 - Physics 111.01 October 6, 2008 PS 6a Problem 1 =...

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