A rigid body is said to be in translational equilibrium, if it remains at rest or moving with a constant velocity in a particular direction. For this, the net external force or vector sum of all the external forces acting on the body must be zero, i.e., oversetrarr(F) = 0 or overset rarr(F) = sum overset rarr(F_(i)) = 0 If U is potential energy of the body, then F = - (dU)/(dr) = 0 or U = constant (max. or min.) When U = minimum, equilibrium of body is stable, When U tends to increase, equilibrium is unstable, When U remains constant, equilibrium is neutral. Read the above passage and answer the following questions : (i) When can a bosy moving uniformly along a straight line be in equilibrium ? What is this equlilbrium called ? (ii) What is the significance of U = minimum in day to day life ?

A rigid body is said to be in translational equilibrium, if it remains

1.	A rigid body is said to be in translational equilibrium, if it remains at rest or moving with a constant velocity in a particular direction. For this, the net external force or vector sum of all the external forces acting on the body must be zero, i.e., oversetrarr(F) = 0 or overset rarr(F) = sum overset rarr(F_(i)) = 0 If U is potential energy of the body, then F = - (dU)/(dr) = 0 or U = constant (max. or min.) When U = minimum, equilibrium of body is stable, When U tends to increase, equilibrium is unstable, When U remains constant, equilibrium is neutral. Read the above passage and answer the following questions : (i) When can a bosy moving uniformly along a straight line be in equilibrium ? What is this equlilbrium called ? (ii) What is the significance of U = minimum in day to day life ?
Answer» Solution :(i) A body moving UNIFORMLY along a straight line is in equilibrium when VECTOR sum of all the external forces acting on the body is zero. This equilibrium is called dynamic equilibrium. (ii) When `U =` minimum, i.e. potential energy of the body is minimum, the body is in stable equilibrium. In day to day life, stable equilibrium CORRESPONDS to peace of mind and potential energy `(U)` corresponds to your involvement. THUS when your involvement is minimum, you have peace of mind and stability.