A tube of length L is filled completely with an incompressible liquid of mass M and closed at both the ends. The tube is then rotated in a horizontal plane about one of its ends with a uniform angular velocity . The force exerted by the liquid at the other end is
- ML2 22
- ML 22
- ML2 2
- ML 2
Answer
(2) ML 22
Solution
Mass per unit length of the liquid = ML.
Consider an element of length dx at a distance x from the axis: dm = MLdx
centripetal force needed by it, dF = (dm) 2 x = ML 2 x dx
This force is finally supplied by the closed far end of the tube, so the liquid presses on that end with
F = 0L ML 2 x dx
= M 2L L22
= ML 22
(Equivalently, the whole mass M moves as if concentrated at its centre of mass at L2.)
Answer: (2)