EXAMPLE 8.2 The Swinging Door (a) Top view of a door being pushed by a 300 N for

Question

EXAMPLE 8.2The Swinging Door (a) Top view of a door being pushed by a 300 N force. (b) The components of the 300 N force. SOLUTION Substitute into the general torque equation. Set the sum of the torques equal to zero. ?hinge+?wedge+?F= 0 Set the sum of the torques equal to zero. ?hinge+?wedge+?F= 0 The hinge force provides no torque because it acts at the axis (r= 0). The wedge force acts at an angle of-90.0?,oppositeFy. Fwedge=347 N LEARN MORE RemarksNotice that the angle from the position vector to the wedge force is -90?. This is because, starting at the position vector, it's necessary to go 90? clockwise (the negative angular direction) to get to the force vector. Measuring the angle in this way automatically supplies the correct sign for the torque term and is consistent with the right-hand rule. Alternately, the magnitude of the torque can be found and the correct sign chosen based on physical intuition. Figure b illustrates the fact that the component of the force perpendicular to the lever arm causes the torque.

QuestionTo make the wedge more effective in keeping the door closed, should it be placed closer to the hinge or to the doorknob? closer to the hingecloser to the doorknob
Why? (Select all that apply.)
to increase the torque that results from each newton of force the wedge exertsto decrease the distancerthat determines the torque from the forceto decrease the torque that results from each newton of force the wedge exertsto increase the distancerthat determines the torque from the force
LEARN MORE RemarksNotice that the angle from the position vector to the wedge force is -90?. This is because, starting at the position vector, it's necessary to go 90? clockwise (the negative angular direction) to get to the force vector. Measuring the angle in this way automatically supplies the correct sign for the torque term and is consistent with the right-hand rule. Alternately, the magnitude of the torque can be found and the correct sign chosen based on physical intuition. Figure b illustrates the fact that the component of the force perpendicular to the lever arm causes the torque.

QuestionTo make the wedge more effective in keeping the door closed, should it be placed closer to the hinge or to the doorknob? closer to the hingecloser to the doorknob
Why? (Select all that apply.)
to increase the torque that results from each newton of force the wedge exertsto decrease the distancerthat determines the torque from the forceto decrease the torque that results from each newton of force the wedge exertsto increase the distancerthat determines the torque from the force
closer to the hingecloser to the doorknob to increase the torque that results from each newton of force the wedge exertsto decrease the distancerthat determines the torque from the forceto decrease the torque that results from each newton of force the wedge exertsto increase the distancerthat determines the torque from the force PRACTICE IT EXERCISEHINTS:GETTING STARTED|I'M STUCK! ?=N ? m

Explanation / Answer

h-x=3.23-.544=2.686 m

cos theta sqrt(8.59)^2-(2.868)^2/8.59=.95m

torqu=(81500)(.95)(3.23)=2.50x10^5 N.m

Thanks.

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