InClassLecture25 - 9-86* A rope attached to a ZZO—kg...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 2
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 9-86* A rope attached to a ZZO—kg block passes over a fixed drum as shown in Fig. P9—86. If the coefficient of friction between.the rope and the drum is 0.30, determine (a) The minimum force fi that must be used to keep the block from falling. (b) The minimum force § that must be used to begin to raise the block. Fig.P9-86 SOLUTION From a free-body diagram for the block: ‘Y’ +T2Fy=T—mg=0 T = mg = 220(9.807) = 2158 N W3 From Eq. 9—16b: _ MB _ o.3o(n/2) _ T2 — Tie — Tie — 1.6020'1‘1 (a) During lowering of the block: T2 = 2158 N T2 2158 Pmin = T,1 = m = m = 1347.1 N g 1347 N Ans. (b) During raising of the block: T1 = 2158 N P , = T = 1.6020T1 = 1.6020(2158) = 3457 N ¥ 3460 N Ans. min 2 9—89 The electric motor shown in Fig. P9-89 weighs 30 lb and delivers 50 in.-lb of torque to pulley A of a furnace blower by means of a V—belt. The effective diameters of the 36 pulleys are 5 in. The coefficient of friction is 0.30. Determine the minimum distance a to prevent slipping of the belt if the rotation of the motor is clockwise. SOLUTION . _ ___Ji___., __Jlfi¥L__ _ For a pulley' “enh ' sin («/2) ‘ sin (36/2) “ 0'9708 u 5 = 0.9708(n) = 3.050 enh From Eq. 9—17: T2 = T1e3'050 = 21.11T1 From a free-body diagram for the blower pulley: + D 2MB = Tarp — TirP — cA 21.11T1(2.5) — T1(2.5) - 50 = 0 T = 0.9945 lb T = 21.11T1 21.1l(0.9945) = 20.99 lb From a free-body diagram for the motor: + C EMA = T2(8 + rP) + T1(8 - pp) — WM(a) = 20.99(10.5) + 0.9945(5.5) — 30a = 0 7.529 in. E 7.53 in. Ans. 9: u 9-90 The band brake of Fig P9-90 is used to control the rotation of a drum. The coefficient of friction between the belt‘and the drum is 0.35 and the weight of the handle is 15 N. If a force of 200 N is applied to the end of the handle, determine the maximum torque for which no motion occurs if the torque is applied (a) Clockwise. (b) Counterclockwise. SOLUTION 180 + 30 360 3.665 rad. (211') B: 0.35(3.665) = 1.2828 #3 = From Eq. 9-16b: . 8 T =Te =Te1282 = 2 1 1 3.6067T1 (a) From a free-body diagram of the handle when the rotation of the drum is 200N clockwise: + C EMA = 200(675) — 15(225) — T2(75) = 0 T2 = 1755.0 N T l _ 2 _ 1755.0 _ 1 T1 ' 3.607 ‘ 3.606 ' 486‘6 N Tmax = (T2 - T1)R = (1755.0 - 486.6)(0.150) = 190.3 N'm Ans T, 200); (b) From a free—body diagram of the handle when the rotation of the drum is counterclockwise: WSantl T2 = 1755.0 N n 5 \s N T2 = 3.6067T1 = 3.6067(1755.0) = 6329.8 N T = (T2 - T1)R = (6329.8 — 1755.0)(0.150) = 686 N'm Ans. 9-96* A 100—N crate is sitting on a ZOO—N crate as shown in Fig. P9-96. The rope that joins the crates passes around a frictionless pulley and a fixed drum. The coefficient of friction is 0.30 at all surfaces. Determine the minimum force F that must be applied to the ZOO-N crate to start motion. SOLUTION L2“ ,1“ From a free—body diagram .T -r of the 100—N crate: g I . . . . m "I For impending sllding: No )ooN 3 )ooN + T XFy = An — 100 = 0 __ n B A = 100 N R «3’ Bn " "n A =uA =0.3(100> =30N u TVqu f n For impending tipping: + C 2MB = T(2.5) - 100(0.6) = 0 T = 24 N < 30 N (crate tips) 'yi From Eq. 9—16b: T2 : T1eu6 = 24eo.3o(2N/3) = 45 N From a free-body diagram of the ZOO—N crate: 5" cn=300N + —e ZFX = P — Af - Cf - T2 = 0 P , = Ar + Cf + T2 = 24 + 0.3(300) + 45 = 159.0 N Ans. Min ...
View Full Document

Page1 / 4

InClassLecture25 - 9-86* A rope attached to a ZZO—kg...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online