Question

nasa has recently sent several spacecraft, call rovers, to mars to explore the planet’s surface. one of these rovers has a mass of about 900 kilograms. the mass of mars is about one - tenth the mass of earth.
○ its weight is higher on mars because the density of mars is greater than the density of earth.
○ its weight is the same on mars because its mass remains the same on both planets.
○ its weight is zero on mars because mars lacks a gravitational field.
○ its weight is lower on mars because the mass of mars is smaller than earth’s mass.

Explanation:

1. Analyze the first option: Mars' density is less than Earth's, and weight depends on gravity (related to planet's mass), not just density. So this is wrong.
2. Analyze the second option: Weight is the force due to gravity ($W = mg$), and $g$ (acceleration due to gravity) differs on Mars and Earth. Mass is constant, but weight depends on $g$, so weight isn't the same. This is wrong.
3. Analyze the third option: Mars has a gravitational field (it has gravity, as rovers land on it), so weight can't be zero. This is wrong.
4. Analyze the fourth option: Weight $W = mg$, where $g$ is proportional to the planet's mass (from Newton's law of gravitation, $g\propto \frac{M_{planet}}{r_{planet}^2}$). Since Mars' mass is smaller than Earth's, $g$ on Mars is smaller, so weight ($W = mg$ with constant $m$) is lower on Mars. This is correct.

Answer:

The correct option is: Its weight is lower on Mars because the mass of Mars is smaller than Earth’s mass.