The drawing shows the top view of two doors. The doors are uniform and identical. Door A rotates about an axis through its left edge, and door B rotates about an axis through its center. The same force is applied perpendicular to each door at its right edge, and the force remains perpendicular as the door turns. No other force affects the rotation of either door. Starting from rest, door A rotates through a certain angle in 3.90 s. How long does it take door B (also starting from rest) to rotate through the same angle?

Question

bobpursley · Answer

torque=moment*accelerationangular

torque=force*distance.

now, the distance of the arm on the second door is 1/2, and the moment is 1/4 (look that up).

so acceleration must be 2/(1/4)=8 x

or the time is 1/8. check my thinking.