Question

A medical suspension bottle is shaken well to disperse the sediment uniformly and immediately, the bottle is gently placed on a digital weighing machine. If $W$ be the actual combined weight of the bottle and the medicine, then the weight recorded by the weighing machine immediately after placing the bottle will be

• A. more than $W$
• B. less than $W$
• C. equal to $W$
• D. nothing can be said

Answer 1

The correct option is B less than $W$

Consider the FBD of the bottle after shaking and keeping on the balance. Now, after shaking the suspended particles being heavier will again start settling down. Thus, the centre of mass of the system must have a downward acceleration.
Now,
$Mg-N=Ma$
$\Rightarrow N=Mg-Ma<Mg$
Thus, weight recorded is less than W.