Question

If the net torque on an object is zero,

a. the object could be accelerating linearly but it could not be rotating.

b. the forces on the object must add up to zero.

c. the object could be both accelerating linearly and rotating.

d. the object cannot be accelerating linearly.

e. the object must be at rest.

(please explain)

Answer 1

a) Since torque is always about some point, if there's a net force on an object you can always find some point about which there will be a torque. So the object can rotate wrt a different point.

b) If net torque on a system is zero does not imply that net force will be zero. For example if two unequal forces are acting at the centre of a rim, then torque is zero on the system but net force is not.

the object cannot be accelerating

c) Yes it is also possible.. Think an electric dipole in an non-uniform dekh har.

d) The object may be accelerate as the net forcre need not to ve zero..

e) No need for the object to be at rest