Question

A small spacecraft has a mass mo = 5.0 x 104 kg when measured at rest. The pilot departs from a research station and accelerates uniformly for 195 days (according to the pilot). The engines provide the pilot with a constant acceleration of g during the journey.

After 195 days of constant acceleration, the pilot notes that the spacecraft is traveling away from the research station at a speed of v = 0.50c. According to the pilot What is the spacecraft’s mass (in kg)?

Answer 1

The question asks the mass of spacecraft according to the pilot who is also moving along with the spacecrafts with same speed. Therefore, for the pilot, there is no change in rest mass. In other words, the rest mass or the mass is

Note that the mass of a body will not change in a frame which is also moving along with the body. The mass will be different from rest mass if the frame of reference has non zero relative velocity with respect to the frame attached with the moving body.