In July 1994 the Comet Shoemaker-Levy 9 struck the planet Jupiter at a speed of around 60km s$^{-1}$ . Although it broke up before impact, the core of the original comet was around 5 km diameter. Its estimated density was $0.3 - 0.7$ g cm$^{-3}$ .
Imagine that such a comet had struck the earth. How much would it have changed the earth's velocity relative to the sun? (Note that the mass of the earth is about $6\times 10^{24}$ kg).