Simultaneity

Lorentz transformations are based on the principle of consistency of the velocity of light.

What would be the mass of body at rest, if it explodes into two objects of mass $2 \mathrm{Kg}$ each moving with a speed of $0.8 \mathrm{C}$ relative to the original body?

The dynamic mass of electron having rest mass ${\mathrm{m}}_{\mathrm{o}}$ and moving with speed $0.8\mathrm{C}$ is 

Two particles approach each other with a velocity of $0.9 \mathrm{C}$. What is their relative velocity as observed by $\mathrm{A}$?

When a particle is moving with a velocity of light $\mathrm{C}$ relating to $\mathrm{S}$ its velocity as observed by an observer in the frame $\mathrm{S}\text{'}$is-

Two particles approach each other with a speed $0.8\mathrm{C}$ w.r. to the laboratory. Their relative speed is 

A spaceship is launched from earth surface with a velocity of $0.3c$. It fires a rocket with a velocity of $0.6c$ relative to spaceship away from the earth. What will be the velocity of rocket observe from Earth’s surface? In the above case, The velocity as observed from the rocket surface is _____$c$. (Write the answer up to two decimal places)