A warehouse worker is pushing a 90.0-kg crate with a horizontal force of 276 N a

Question

A warehouse worker is pushing a 90.0-kg crate with a horizontal force of 276 N at a speed of v = 0.880 m/s across the warehouse floor. He encounters a rough horizontal section of the floor that is 0.75 m long and where the coefficient of kinetic friction between the crate and floor is 0.353.

(a) Determine the magnitude and direction of the net force acting on the crate while it is pushed over the rough section of the floor. magnitude _________N

direction=_______________

(b) Determine the net work done on the crate while it is pushed over the rough section of the floor. _____________J

(c) Find the speed of the crate when it reaches the end of the rough surface. ______________m/s

Explanation / Answer

a) in vertical,

N - mg = 0

N = 90 x 9.8 = 882 N

friction force, f = uk N = 0.353 x 882 = 311.35 N

in horizontal,

Fnet = F - f = 276 - 311.35 = - 35.35 N

(minu sign indicates that direction of Fnet in left side)

b) W = Fnet. d

angle between Fnet and d is 180 deg

W = Fnet d cos180 = - Fnet d

= - 35.35 * 0.75 = - 26.5 J

c) USing work energy theorem,

work done = change in KE

-26.5 = 90 vf^2 /2 - 90 (0.880^2 / 2)

vf = 0.43 m/s

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