Question

7. An aluminum wire 1.0 m in length and 2.0 mm in diameter supports a 10.0-kg mass. What is the elongation of the wire? (The Young's modulus for an aluminum is 7.0 × 1010 N/m2)

3. Two equal forces are applied to a door. The first force is applied at the midpoint of the door; the second force is applied at the doorknob. Both forces are applied perpendicular to the door. Which force exerts the less torque?

Answer 1

Solution :

(7)

(3) The hinge is the axis of rotation in both cases.

Now, the midpoint of the door is closer to the hinge compared to the doorknob.

Also, torque is directly propotional between the distance of point of application of force and the axis of rotation.

Hence, the first force will produce less torque, since it is applied closer to the axis of rotation.