The small car, which has a mass of $20 \mathrm{kg},$ rolls freely on the horizontal track and carries the $5-\mathrm{kg}$ sphere mounted on the light rotating rod with $r=$ $0.4 \mathrm{m} .$ A geared motor drive maintains a constant angular speed $\dot{\theta}=4$ rad/s of the rod. If the car has a velocity $v=0.6 \mathrm{m} / \mathrm{s}$ when $\theta=0,$ calculate $v$ when $\theta=60^{\circ}$. Neglect the mass of the wheels and any friction.