1. The problem statement, all variables and given/known data The two blocks in the figure are connected by a massless rope that passes over a pulley. The pulley is 16cm in diameter and has a mass of 1.3kg. As the pulley turns, friction at the axle exerts a torque of magnitude 0.50 N*m. If the blocks are released from rest, how long does it take the 4.0kg block to reach the floor? Express your answer using two significant figures. 2. Relevant equations τ = Iα I = (1/2)MR2 = (1/2)(1.3kg)(0.082) = 0.00416 kg*m2 mpulley = 1.3kg rpulley = (16/2)cm = 8cm = 0.08m 3. The attempt at a solution a. Find the net torque being exerted on the pulley: Στ = τm1 - τm2 - τƒ = Fm1*r*sin(90) - Fm2*r*sin(90) - 0.5 N*m = (4.0kg)(9.8m/s2)(0.08m) - (2.0kg)(9.8m/s2)(0.08m) - 0.5 N*m = 3.136 N*m - 1.568 N*m - 0.5 N*m = 1.068 N*m b. Find the angular acceleration α of the pulley: Given τ = Iα, α = τ/I = (1.068 N*m) / (0.00416 kg*m2) = 256.73 rad/s2 (this seems very large to me) c. Given the radius of the pulley and α, we can now find linear acceleration: a = rα = (0.08 m)(256.73 rad/s2) = 20.54 m/s2 d. Use the kinematic equation to find the final velocity after the block travels 1m to the floor: v2 = v02 + 2ax v2 = 2ax = 2(20.54 m/s2)(1.0 m) = 41.08 v = 6.41 m/s e. Now substitute v into the definition of velocity and solve for Δt: v = Δx/Δt Δt = Δx / v = (1.0 m) / (6.41 m/s) = 0.16s (rounded to 2 sig figs) My homework system says this answer is wrong. I am not sure why I keep getting the wrong answer. Can someone help me out here? It is much appreciated.