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# Monthly Archives: July 2016

## Determine the current in the resistors. Kirchoffs law

Determine the current in the resistors in the following circuit using Kirchhoff’s laws

## 2 different types of sublimation

I’m trying to get the right terms for various forms of phase change. I am familiar with the phase change / triple point diagram for ice, but I have a question. For example we have various terms for the transition of a liquid or solid to a gas, such as boiling, evaporation, vaporization, sublimation. There seems to be a clear distinction between the 2 types of transition between a liquid and a gas: One happens when the substance, let’s say water, boils or vaporizes at it’s boiling point (that varies with pressure of course) and the other type, called evaporation, which occurs at almost any temperature below the boiling point, but it just happens more slowly than boiling. So those 2 types are clear: Boiling / Vaporization vs Evaporation.
However my question relates to the 2 types of phase change which occur when ice changes to gas. I can only find the one word sublimation, however, there are also 2 distinct types of sublimation, that which occurs at the exact temperature (dependent on the pressure), and similar to boiling, it happens rapidly until all the ice is gone (if enough heat is available) – but then there is an analogous change similar to evaporation, where the process is slower because the change from ice to gas can happen at almost any temperature lower than the sublimation temperature. I don’t want to make up a term such as “evaporative sublimation” unless there is really such a term. Can anyone enlighten me on this.

## Bullet shot in space, will it move forever … ?

if i fire a bullet in space it will move forever (assuming it won’t hit any celestial object and doesn’t get caught by any aliens). But will it accelerate forever and reach 0.99c or will it accelerate till it attain a certain constant velocity?

Akshay Ramachandran First, there should be something to accelerate the bullet, like some propellant or else if no forces act on it, it moves with a constant speed. But assuming that it is accelerating, then as it increases its speed, the apparent mass of it increases making it difficult for it to accelerate. This can be said in different languages, like the time in its reference becomes slow etc etc. All this stems from theory of relativity whose basic principle is that speed of light is constant independent of the frame of reference because of Maxwell’s law….As a result it won’t reach the speed of light.
Now the next question would be to what speed would it accelerate? The basic answer lies in the amount of propellant you are having. In space to it would be foolish to assume that force experienced by bullet would be constant? There is gravity everywhere which would try to accelerate/decelerate or divert the bullet. Hence it would never be increasing its speed. It requires a lot of propulsion for that and you can calculate the amount of force required to increase the speed of an object from 0 m/s to 0.99 c m/s by integrating using expression of mass as function of velocity

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