Final answer:
A satellite is placed in a circular orbit to observe the surface of Mars by continuously falling towards the planet due to gravity, while also moving forward with enough speed to maintain a circular path.
Step-by-step explanation:
A satellite is placed in a circular orbit to observe the surface of Mars. When a satellite is in orbit around a planet, it is constantly falling towards the planet due to the force of gravity. However, the satellite is also moving forward with enough speed to continuously miss the planet and maintain a circular path. This combination of falling and forward motion creates a balance, allowing the satellite to stay in orbit and observe the surface of Mars.