Turning Effects of Forces

Which statement best describes a couple?

• a pair of forces of equal magnitude acting in opposite directions which produce rotational

  motion but not translational motion

• a pair of forces of equal magnitude acting in opposite directions which produce translational motion but not rotational motion

• a pair of forces of equal magnitude acting in the same direction which produce rotational motion but not translational motion

• a pair of forces of equal magnitude acting in the same direction which produce translational motion but not rotational motion

A uniform rod XY of weight 10.0 N is freely hinged to a wall at X. It is held horizontal by a force F acting from Y at an angle of 30° to the horizontal, as shown. What is the value of F ?

• 5.0 N

• 8.7 N

• 10.0 N

• 20.0 N

Two forces, each of magnitude F, act along the edges of a rectangular metal plate, as shown. The plate has length a and width b. What is the torque about point P?

• Fa

• Fb

• 2Fa

• 2Fb

A non-uniform rod has a mass of 100 g and a length of 50 cm. It is supported by a chain at its midpoint. The rod is held in equilibrium by having a mass of 60 g suspended from its right-hand end, as shown.

The centre of gravity of the rod is a distance d from its left-hand end. What is the value of d ?

• 10 cm

• 15 cm

• 25 cm

• 40 cm

Which pair of forces forms a couple with a torque of 30 Nm?

• A

• B

• C

• D