4. -15 points KatzPSEf1 9.P.052. My Notes Ask Your Teacher A horizontal spring w

Question

4. -15 points KatzPSEf1 9.P.052. My Notes Ask Your Teacher A horizontal spring with force constant k = 695 N/m is attached to a wall at one end and to a block of mass m = 2.80 kg at the other end that rests on a horizontal surface. The block is released from rest from a position 3.40 cm beyond the spring's equilibrium position. (a) If the surface is frictionless, what is the speed of the block as it passes through the equilibrium position? m/s 0.200, what is the speed of the block as it passes through the (b) If the surface is rough and the coefficient of kinetic friction between the box and the surface is Hk equilibrium position? m/s 5. 12 points KatzPSEf1 9.P.065.MI. My Notes Ask Your Teacher Figure A shows a crate attached to a rope that is extended over an ideal pulley. Boris pulls on the other end of the rope with a constant force until the crate has risen a total distance d of 6.30 m as shown in figure B. If the crate has a mass of 81.50 kg, what is the average power exerted by Boris, assuming he accomplishes the task in 5.70 s? A. B.

Explanation / Answer

4.

(A)Applying work - energy theorem,

Work done by spring = change in KE

695 (0.034^2) / 2 = 2.80 v^2 /2

v = 0.536 m/s ........Ans

(B) Work done by spring + work done by friction = change in KE

695(0.034^2)/2 + (-0.20 x 2.80 x 9.8 x 0.034) = 2.80 v^2 / 2

v = 0.392 m/s

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