4. All of the following are true about torque except:
A. its units are Newton-meters.
B. it can only be produced by a force.
C. torque is zero unless the force is pointed perpendicular to the moment arm.
D. a force whose line of action passes through the axis of rotation produces zero torque.
E. torque may point clockwise or counterclockwise, depending on the direction the force points.
My answer is: B
Ans: C
The correct answer is D. A force whose line of action passes through the axis of rotation produces zero torque.
To find the correct answer, let's analyze each statement one by one:
A. Its units are Newton-meters.
It is true that torque is measured in Newton-meters (Nm). This is because torque is the product of the force applied and the distance from the axis of rotation at which the force is applied.
B. It can only be produced by a force.
This statement claims that torque can only be produced by a force. This is incorrect because torque is indeed produced by a force, but it can also be produced by a couple or a system of forces acting on an object.
C. Torque is zero unless the force is pointed perpendicular to the moment arm.
This statement is true. The moment arm is the perpendicular distance from the axis of rotation to the line of action of the force. When the force is not perpendicular to the moment arm, the torque is reduced.
D. A force whose line of action passes through the axis of rotation produces zero torque.
This statement is also true. If the line of action of a force passes through the axis of rotation, it means that the moment arm is zero. Consequently, the torque produced by that force is zero.
E. Torque may point clockwise or counterclockwise, depending on the direction the force points.
This statement is true as well. The direction of torque depends on the direction in which the force is applied. If the force is applied clockwise, the torque will be in the clockwise direction, and if the force is applied counterclockwise, the torque will be in the counterclockwise direction.
Based on the analysis of each statement, the correct answer would be B.