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A 18.0-m length of hose is wound around a reel, which is initially at rest. The

ID: 1261095 • Letter: A

Question

A 18.0-m length of hose is wound around a reel, which is initially at rest. The moment of inertia of the reel is 0.400 kgm2, and its radius is 0.200 m. When turning, friction at the axle exerts a torque of magnitude 3.40 Nm on the reel. If the hose is pulled so that the tension in it remains a constant 26.0 N, how long does it take to completely unwind the hose from the reel? Neglect the mass of the hose, and assume that the hose unwinds without slipping.

A 18.0-m length of hose is wound around a reel, which is initially at rest. The moment of inertia of the reel is 0.400 kg.m2, and its radius is 0.200 m. When turning, friction at the axle exerts a torque of magnitude 3.40 N.m on the reel. If the hose is pulled so that the tension in it remains a constant 26.0 N, how long does it take to completely unwind the hose from the reel? Neglect the mass of the hose, and assume that the hose unwinds without slipping.

Explanation / Answer

Length of the hose is L = 18.0 m

radius r = 0.200m

moment of inertia I = 0.400 kg m^2

circumference = 2?r

                       = 2? * 0.200 m

                       = 1.2566 m

Total angle of rotation is 18.0 m / 1.2566 * 2?

                                       = 90 rad

torque = moment of inertia * angular acceleration

     3.40 N m =   0.400 kg m^ 2 * ?

         ? = 8.5 rad /s^2

w = w_0t +1/2 ? t^2

90 rad = 0 + 1/2 * ( 8.5 ) * t^2

         t = 4.602 s

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