Assertion The angular momentum of system always remain constant.

Reason For a system, $$\tau_{\mathrm{ext}}=\frac{d L}{d t}=0$$

A boy is pushing a ring of mass $$3 \mathrm{~kg}$$ and radius $$0.6 \mathrm{~m}$$ with a stick as shown in figure. The stick applies a force of $$3 \mathrm{~N}$$ on the ring and rolls it without slipping with an acceleration of 0.4 m/s$$^2$$. The coefficient of friction between the ground and the ring is large enough that rolling always occurs and the coefficient of friction between the stick and the ring is $$\frac{F}{10}$$. The value of $$F$$ is

Assertion : The total kinetic energy of a rolling solid sphere is the sum of translational and rotational kinetic energies.

Reason : For all solid bodies, total kinetic energy is always twice of translational kinetic energy.