A particle is projected from the surface of the earth with a speed equal to twice the escape speed. When it is very far away from the earth, what is its speed. (Neglect air resistance.)

What kind of system allows energy to be transferred in and out, but prevents mass from being transferred?

An astronomer on the Earth observes a meteoroid inthe southern sky approaching the Earth at a speed of0.800c. At the time of its discovery the meteoroid is20.0 ly from the Earth. Calculate (a) the time intervalrequired for the meteoroid to reach the Earth as measuredby the Earthbound astronomer, (b) this timeinterval as measured by a tourist on the meteoroid,and (c) the distance to the Earth as measured by thetourist.