Question

Assertion: Water in a $U$-tube executes SHM, the time period for mercury filled up to the same height in the $U$-tube be greater than that in case of water.
Reason: The amplitude of an oscillating pendulum goes on increasing.

• A. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion
• B. If both Assertion and Reason are true but the Reason is not the correct explanation of the Assertion
• C. If Assertion is true but Reason is false
• D. If both Assertion and Reason are false

Answer 1

Answer: (D)

The period of the liquid executing $SHM$ in a $U$-tube does not depend upon the density of the liquid. Therefore, time period will be the same, when mercury is filled up to the same height as the water in the $U$-tube. Now, as the pendulum oscillates, it drags air along with it. Therefore, its kinetic energy is dissipated in overcoming viscous drag due to air and hence, its amplitude goes on decreasing.