Why do we need to know the centre of mass of an object ? For which objects, its position may differ from that of the centre of gravity

What kind of simple machine is a catapult?

Identify the correct relation showing that the radius r of the orbit of a moon of a given planet can be determined from the radius r of the planet, the acceleration of gravity at the surface of the planet, and the time τ required by the moon to complete one full revolution about the planet. determine the acceleration of gravity at the surface of the planet jupiter knowing that r = 71 492 km and that t= 3.551 days and r= 670.9 × 10^3 km for its moon europa.

The dominant wavelength of energy emitted by the sun is