Spot the false rotation claim

Exercise and reference answers

Questions

1. False statement

   A body in translational equilibrium must also be in rotational equilibrium.

   Statements

   1. A rigid body in mechanical equilibrium has neither linear acceleration nor angular acceleration.
   2. A couple leaves the total external force zero while the total torque stays non zero.
   3. A body in translational equilibrium must also be in rotational equilibrium.

2. False statement

   The internal forces of an exploding shell push its centre of mass off the parabola.

   Statements

   1. The internal forces of an exploding shell push its centre of mass off the parabola.
   2. The centre of mass moves as if every external force were applied at that one point.
   3. Zero total external force keeps the total linear momentum of the system constant.

3. False statement

   Moment of inertia depends only on mass, never on which axis is chosen.

   Statements

   1. The SI unit of moment of inertia is kilogram metre squared.
   2. Moment of inertia depends only on mass, never on which axis is chosen.
   3. The centre of gravity is the point where the total gravitational torque is zero.

Instructions

Read the three claims in each round and tap the one that is false.

Explanation