He would die.
The mass of an object weighing 63 N on Earth would be 6.43 kg. This is calculated by dividing the weight (in Newtons) by the acceleration due to gravity (9.81 m/s^2).
A kilogram is equals to 2.20462 pounds. An object weighing 55.8kg would weigh 123lbs.
Mach is the speed of an object expressed as a multiple of the speed of sound in the same medium. Thus, an object travelling at 686 metres per second through air, at sea level, is travelling at Mach 2 because sound would travel through it at 343 m/s. However, it the object was travelling under water at the same speed then it would be travelling at approx Mach 0.46 since sound travels at 1484 m/s through water.
nothing would happen
You compare its mass with something of known mass. In everyday earthbound conditions, this would mean weighing it on a set of weighing scales or on a spring balance.
it would become longer
It could, if it contained enough air. To float on water, you would need about 1 liter of air for every kilogram you want to keep afloat.
it is impossible to fire a bullet a the speed of light
The object would behave as a part of fluid and it will remain where it is kept.
No. For you to know the distance you need to know the time the object has been travelling and a function describing the speed of the object for the time it has been travelling. A direction is not required. correct but you missed direction can affect speed as climbing altitude would get slowed by gravity
The object would float in a given liquid.
The object would crash into the planet.