At a construction site, a 68.0 kg bucket of concrete hangs from a light (but str

Question

At a construction site, a 68.0 kg bucket of concrete hangs from a light (but strong) cable that passes over a light friction-free pulley and is connected to an 85.0 kg box on a horizontal roof (see the figure (Figure 1) ). The cable pulls horizontally on the box, and a 48.0 kg bag of gravel rests on top of the box. The coefficients of friction between the box and roof are shown. The system is not moving.

Part A

Find the friction force on the bag of gravel.

Express your answer using two significant figures.

Part B

Find the friction force on the box.

Part C

Explanation / Answer

The friction force on the bag of gravel is zero since there is no other horizontal force on the bag for friction to oppose. the static friction force on the box equals the weight of the bucket 666.4 N

(c)

m b g y1 - f1 d = 1/2 m t v^2

v = sqr 2/ mt ( m bgy1- uk m box gd)

= sqrt 2/153 ( 68(9.8)(1.8) - ( 0.4)( 80 kg )( 9.8) ( 1.8)

=2.88 m/s

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