Answer to Question #164470 in Physics for Lex

Question

Part 1. Conceptual Questions:

1. Two children at a park sit on opposite ends of a see-saw. The first child sits closer to the center of  the see-saw. Which weighs more, the first child of the second? (if the see-saw is at rest with both ends off the ground); Justify your answer.

2. What factors affect the torque created by a force relative to a specific pivot point? 

a. How close to the ends of the axis the force is applied

b. How far away from the axis the force is applied

c. The size of the object applying the force

d. The size of the force

e. The direction of the force.

Justify your answer.

Part 2. Computation.

3. A bamboo pole 6 m long weighs 300 N. It can be balanced at a point 2.5 m from the thicker end.  If it were to be supported at its ends, how much force would be needed at each end?

4. When opening a door, you push on it perpendicularly with a force of 55.0N at a distance of  0.850m from the hinges. What torque are you exerting relative to the hinges?

5. (b) Does it matter if you push at the same height as the hinges?

Answer 1

1. The one who sits closer to the center weights more because the torque is weight times lever.

2. The correct answers are b, d (if 'size' means 'magnitude'), e because the torque includes two values: lever (distance from the axis to the point where the force is applied) and force.

4. The torque is

$$\tau=55·0.85=46.8\text{ N}·\text{m}.$$

5. It does not matter because the lever is the distance between the axis, not hinge, and the force