# How fast must you travel to get to Sirius in 15.5 years?

1. Apr 13, 2016

### ah011

• Thread moved from the technical forums, so no HH Template is shown.
Question:

Sirius is about 9.50 ly from Earth. To reach the star by spaceship in 15.5 y (ship time), how fast must you travel? Answer in terms of "c".

0.4843c and 0.6129c are incorrect

Relevant Equations and Constants:

Attempt at solution:

Can anyone help out I really don't know what else to do with this problem.

2. Apr 13, 2016

### nasu

You assumed the speed is 0.61 c.
In what reference frame would that speed be?

3. Apr 13, 2016

### ah011

From the work, 0.61c was the result of dividing 9.5/15.5.

4. Apr 13, 2016

### nasu

But these values are not measured in the same frame.

5. Apr 13, 2016

### ah011

If you are referring to unit of measurement, then I honestly don't know how ly and y should be changed. I thought that this was correct way to solve it.

6. Apr 13, 2016

### nasu

Nothing to do with units. Did you learn about reference frames? The meaning of Lorentz transformations?
I suppose you should have posted this in the homework section, anyway,

7. Apr 13, 2016

### Keiran OConnor

Why wasn't this answered ?

8. Apr 13, 2016

### SammyS

Staff Emeritus
@Keiran OConnor,
Who is your question directed at ?

9. Apr 13, 2016

### Keiran OConnor

Nasu he seemed to know the answer or at least the formula but wouldn't tell him ?

10. Apr 13, 2016

### nasu

11. Apr 13, 2016

### SammyS

Staff Emeritus
nasu is attempting to guide ah011 to a solution .

12. Apr 13, 2016

### Keiran OConnor

So on one hand (the rules) conform.
The other hand possibly (assuming) a young enthusiastic student not getting a answer because of bureaucratic procedures.

You made it clear that he was posting in the wrong part of the forum, ok that's fine. Are we just ignoring the question/person now ?

13. Apr 13, 2016

### Staff: Mentor

Ultimately, simply giving answers rather than guiding the student toward understanding and being able to answer the question (and other similar questions) themself will not benefit the student.

It is now up to the OP (ah011) to engage with the offered guidance in a productive way. If you have further suggested hints or guidance (not direct answers) to offer the OP then you are welcome to join in.