ROTATIONAL MOTION

What is the condition for a rigid body to be in rotational equilibrium under coplanar forces?

• All forces must be equal
• Forces must act at the center
• The sum of the torques about any axis perpendicular to the plane must be zero
• Only one force should act

What happens to the net torque when two equal and opposite forces act at the ends of a rod but are collinear?

• It becomes infinite
• It causes rapid rotation
• The net torque is zero
• It doubles

How does reversing the direction of one force on a rod's end change the system's equilibrium?

• It stops all motion
• It increases the mass
• It changes the length of the rod
• It changes the system from rotational equilibrium to translational equilibrium

Why does a compass needle align itself with the Earth's magnetic field?

• Because the needle is heavy
• Because of gravitational pull
• Because it is painted to point north
• A torque acts on the needle due to a couple formed by magnetic forces until alignment is achieved

What defines a couple in terms of force system?

• Any two forces acting on a body
• Forces that are perpendicular to the motion
• Two forces equal in magnitude, opposite in direction, and separated by a perpendicular distance
• Two forces acting at the same point