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Homework8-F09

Homework8-F09 - Homework8 Chapt 11 12 Delivering Rescue...

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Homework8 Chapt. 11 & 12 Delivering Rescue Supplies You are a member of an alpine rescue team and must project a box of supplies, with mass , up an incline of constant slope angle so that it reaches a stranded skier who is a vertical distance above the bottom of the incline. The incline is slippery, but there is some friction present, with kinetic friction coefficient . Ei(total)-f k Δ S = Ef(total) Ki = 0 , Ui = mgh, f k = μ k N = = μ k mg cos α , Δ S = h/sin α Kf = ½ mV f 2 , Uf = 0 Therefor ½ mV f 2 = mgh - μ k mg cos α ·h/sin α Vf = 2 2 cos / sin k gh gh μ α α + 12.22. Model: The disk is a rotating rigid body. Visualize: The radius of the disk is 10 cm and the disk rotates on an axle through its center. Solve: The net torque on the axle is A A A B B B C C C D D D sin sin sin sin (30 N)(0.10 m)sin( 90 ) (20 N)(0.050 m)sin90 (30 N)(0.050 m)sin135 (20 N)(0.10 m)sin0 3 N m 1 N m 1.0607 N m 0.94 N m F r F r F r F r τ φ φ φ φ = + + + = - ° + ° + ° + ° = - + + = - Assess: A negative torque means a clockwise rotation of the disk. 12.27. Model: Two balls connected by a rigid, massless rod are a rigid body rotating about an axis through the center of mass. Assume that the size of the balls is small compared to 1 m. Visualize:

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We placed the origin of the coordinate system on the 1.0 kg ball.
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