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 47.0 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.

Find the friction force on the box.

Suddenly a worker picks up the bag of gravel. Use energy conservation to find the speed of the bucket after it has descended 1.50 m , from rest. (You can check your answer by solving this problem using Newton's laws.)

Gravel Box Ms = 0.700 MK = 0.400 Concrete

Answer 1

n m, 285 kg m2 = 47 kg 9=10 mis? N = (m, +M2) g = 132 x 10 = 1320 (47+85)9 (mg) : friction face on box is F, = MsN = 0.100 X 1320 = 924N T: friction face on Box = 9240 .

Ę=0.4x850 E=MAN -340N 85 Kg x 10 = 850N. P3 Kg xioms? = 680N - for Ma: Mag-T=mza 0 for m,: Theig - mia. T = Memig+m, a The eplepeabeelle sub ② in ① - mgumig-m, a=mza m, 9 – К. т, а m, tma - a . in a 680 - 340 - 2.22m s-2 68+85 = ? at s=1.5m ; a=2.22 ms 2 u=0 : w²0² + 2as (or conservation of energy. [2 mut-Imut = mas v = 0+ 2x2.22 X 1.5 10=2587/41