$1$ light$-$year is about $9,461,000,000,000$ km $--$ that's $9\mathrm{.}461$ x $10\mathrm{¹²}$² km$.$ Imagine that a spacecraft is launched from Earth to take humans to a newly discovered Earth$-$like planet that is $5\mathrm{.}7$ light$-$years away. How fast would the spacecraft have to travel $($in km$/$hr$)$ in order to reach the planet in $100$ years?

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Distance to the Earthlike planet 57 lightyears 1 lightyear 94... View the full answer