A force 'F' is acting at point 'P' of a uniform rod capable of rotating about 'O'. What is the torque about 'O'?
Correct answer: D. (OP)(F cosϴ)
- A. (OP)(F tanϴ)
- B. (OP)(F)
- C. (OP)(F sinϴ)
- D. (OP)(F cosϴ)
Explanation
Torque is the cross product between the distance vector (the distance from the pivot point to the point where force is applied) and the force vector,It is important that the force being applied is perpendicular to the rotational axis therefore we will use a component of force F which is perpendicular to the rotational axis. Since the angle θ is between the force F and the perpendicular. The force applied on the rotational axis for torque will be Fcosθ.The distance given here is OP and the force applied is Fcosθ.Torque = d x FTorque = (OP)(Fcosθ)
This question appeared on the UHS MDCAT 2012 paper, which you can sit online with every answer explained.
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