To get a door to swing open most rapidly (with greatest angular acceleration), h

Question

To get a door to swing open most rapidly (with greatest angular acceleration), how is it best to apply a force of 1.0 N to the door?

A. At the end closest to the hinges, parallel to the plane of the door

B. At the end closest to the hinges, perpendicular to the plane of the door

C. At the far end from the hinges, parallel to the plane of the door

D. At the far end from the hinges, perpendicular to the plane of the door

E. All of these ways of applying the force will result in the same angular acceleration

Which of the following objects has the lowest rotational inertia?

I. A point mass with mass m at a distance of r from the axis of rotation

II. A hoop with total mass m with diameter 2r rotating around an axis going through the center of the hoop perpendicular to the plane of the hoop

III. A point mass with mass 4m at a distance of r/2 from the axis of rotation.

A. I

B. II

C. III

D. They are all the same

E. I and III

An astronaut in a space station orbiting the Earth floats around inside the space station, neither moving towards the floor or the ceiling. This is because

A. the astronaut has no weight so far from the Earth.

B. there is no way to create a normal force between the astronaut and the floor of the space station.

C. the difference in weight between the astronaut and the space station creates a different centripetal acceleration on the astronaut compared to the space station.

D. nothing has weight while in circular motion because the centripetal force takes its place.

E. the astronaut is in the same orbit as the space station, so they move together.

Explanation / Answer

(1) To get a door to swing open most rapidly, it is best to apply the force at the far end from the hinges, perpendicular to the plane of the door.

(2) They are all the same.

(3) An astronaut in a space station orbiting the Earth floats around inside the space station, neither moving towards the floor or the ceiling. This is because the astronaut is in the same orbit as the space station, so they move together.

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