Final answer:
To reach Sirius in 15.0 years ship time, the spaceship must travel at a speed of 0.600 times the speed of light, which is 60% of the speed of light.
Step-by-step explanation:
To reach Sirius, which is about 9.00 light-years from Earth, in 15.0 years ship time, we need to calculate the required speed for the spaceship. Since distance equals speed times time, we rearrange this to solve for speed as Speed = Distance / Time. The speed of the spaceship must be such that it can cover the distance of 9.00 light-years in 15.0 years of ship time.
To calculate this, we divide the distance by time:
Speed = 9.00 ly / 15.0 y = 0.600c
This means the spaceship must travel at 0.600 times the speed of light, or 60% the speed of light (denoted as c), to reach Sirius in 15 years from the perspective of someone on the spaceship. It is important to note that due to relativistic effects, time would dilate and the perceived time for observers on Earth would be different.