Assertion (A) Angular speed, linear speed and kinetic energy change with time but angular momentum remains…
Assertion (A)
Angular speed, linear speed and kinetic energy change with time but angular momentum remains constant for a planet orbiting the sun.
Reason (R) Angular momentum is constant as no torque acts on the planet.
Both $\mathrm{A}$ and $\mathrm{R}$ are true and $\mathrm{R}$ is a correct explanation for $A$.
Both $\mathrm{A}$ and $\mathrm{R}$ are true but $\mathrm{R}$ is not a correct explanation for $A$.
$A$ is true, $R$ is false.
$A$ is false, $R$ is true.
Solution
As we know that, Torque is the moment of force and torque $(\tau)=\mathbf{r} \times \mathbf{F}$ where, $\mathbf{r}$ is distance between axis of rotation and force $(F)$.
Also, $\tau=\frac{d L}{d t}$
and since, in space there is no external torque is applied so, $\tau=0$
$
\therefore \quad \Delta L=0=\text { constant }
$
Hence, Assertion (A) and Reason (R) both are true and Reason (R) is the correct explanation of Assertion (A)