Final answer:
The astronaut's mass in space remains 74 kg, but their weight decreases to 636.4 N from 725.94 N on Earth due to the lower gravitational field strength. Weight changes with gravity, but mass is constant. Astronauts appear weightless on the ISS due to the microgravity environment caused by orbiting Earth in free-fall.
Step-by-step explanation:
The mass of an astronaut, which is the amount of matter in their body, does not change whether they are on Earth or on the International Space Station (ISS). So, the mass of the astronaut on the station remains 74 kg.
On Earth, the weight of an object is calculated using the gravitational field strength (g = 9.81 N/kg). The astronaut's weight on Earth would be mass times the gravitational field strength, which is 74 kg × 9.81 N/kg = 725.94 N.
On the ISS, with a gravitational field strength of 8.6 N/kg, the astronaut's weight is 74 kg × 8.6 N/kg = 636.4 N. The difference in weight on Earth and the ISS is 725.94 N - 636.4 N = 89.54 N.
The astronaut's weight changes because weight is a measure of the gravitational pull on an object, and this force varies with the local gravitational field strength. However, mass is a measure of the amount of matter in an object and does not depend on gravity.
Astronauts appear weightless on the ISS because they are in free-fall, orbiting Earth. The station and everything inside it, including the astronauts, are falling towards Earth but also moving forward quickly enough that they continuously fall around Earth, rather than directly into it. This creates a microgravity environment where they experience weightlessness.