By learning its composition and the weight of its elements, and computing them with the volume of space they occupy. The size of a planet can be misleading, as Jupiter is much larger than earth but it weighs very little because it is not solid.
Well you would need to know the force of Gravity on the surface of Planet A to answer this. The equation to use would be 5 multiplied by the force of gravity on Planet A = the weight in kilograms. So if Gravity on planet A was twice that on Earth then it would weigh 10Kg and if it was 1/2 that on Earth it would weigh 2.5 kg.
On Jupiter
Jupiter
Jupiter, as it has the most gravity.
pluto
On Mars, you would weigh about 23.7 pounds. On Venus, you would weigh about 58.5 pounds. On Jupiter, you would weigh about 165.3 pounds.
Your mass would remain constant regardless of the planet you are on, as mass is a measure of the amount of matter in your body. However, your weight would change because weight depends on the gravitational force exerted on your mass, which varies from planet to planet. For instance, on a planet with stronger gravity, you would weigh more, while on a planet with weaker gravity, you would weigh less.
There are probably meteors, small asteroids, or tiny comets that might weigh 1225 newtonson the surface of a moon or planet, but no "planet" would. There are people who weigh morethan that!
On Mercury, you'd weigh 28.88 pounds.
Not on any planet in this solar system. Mercury has the weakest gravity of any planet in the solar system. A 100 lb person on Earth would weigh 37 lbs on Mercury. That same person would weigh about 17 lbs on the moon, but the moon is not a planet.
you would weight about 6.4% of what you do on Earth.
This question is harder than it might seem. The answer is: You would weigh less on both Venus and Mars. You would weigh more on Jupiter. As regards Saturn, you could weigh more or less depending where on the planet you were. For example, at Saturn's equator the effect of the planet's rotation would be enough to reduce your effective weight to less than your Earth weight.