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Physics Problems 114

# Physics Problems 114 - the torque 012 qfull 00610 2 3 0...

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110 Chapt. 12 Rotational Dynamics Full-Answer Problems 012 qfull 00350 1 5 0 easy thinking: moment arm 1. The general rule for torque is vector τ = vector r × vector F . However, there is a simple rule that provides an alternative way of calculating the magnitude of the torque. This rule is particularly useful when calculating the torque for forces illustrated on 2-dimensional diagrams. The magnitude of the torque recall is τ = rF sin θ, where θ is the angle between the radius and force vectors. Draw a general radius vector r from an origin to a point where a force vector F is applied. Then find an obviously relevant displacement on the figure that has magnitude r sin θ . This displacement is called the moment arm (HRW-230). Finding the magnitude of the moment arm on a diagram often leads to simple calculation for
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Unformatted text preview: the torque. 012 qfull 00610 2 3 0 moderate math: LLNL door and torque Extra keywords: (HR-243:53p) 2. The shield door of the neutron test facility at Lawrence Livermore National Laboratory (where they design the bombs) is (or was), according to HRW-243, the world’s most massive hinged door: mass 44 , 000 kg, rotational inertia about its hinge axis 8 . 7 × 10 4 kg m 2 , door width 2 . 4 meters. Assuming zero friction, what constant force perpendicular to the door at its outer edge is needed to move the door 90 ◦ in 10 s starting from REST ? Show your calculations. Could you open this door in the time given? Would you want to open this door?...
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