Posted by **Darren** on Thursday, May 5, 2011 at 3:07pm.

Suppose you wish to visit a star which is 450 light years away, and that you want your 21000 kg rocket to move so fast that you only age 20 years during the round trip.

a. How fast must the rocket travel relative to the Earth? Give your answer as the fraction of the speed of light.

b.Assuming your turn-around time is near zero when you reach the star, how long does your trip take according to your friends and family back on Earth?

c.How much energy is needed to accelerate the rocket to this speed?

d.The entire earth uses approximately 5*1020 Joules of energy each year. What is the ratio of you answer to part c to the total Earth's energy usage in one year?

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