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# An alien spaceship traveling at $0.600 c$ toward the Earth launches a landing craft. The landing craft travels in the same direction with a speed of $0.800 c$ relative to the mother ship. As measured on the Earth, the spaceship is 0.200 ly from the Earth when the landing craft is launched. (a) What speed do the Earth-based observers measure for the approaching landing craft? (b) What is the distance to the Earth at the moment of the landing craft's launch as measured by the aliens? (c) What travel time is required for the landing craft to reach the Earth as measured by the aliens on the mother ship? (d) If the landing craft has a mass of $4.00 \times 10^{5} \mathrm{kg}$, what is its kinetic energy as measured in the Earth reference frame?

## $0.946 c$

Gravitation

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