A.2.13—Weight

Weight is a force

Weight is the gravitational force on a mass:

$F_g=mg$

The direction is toward the local gravitational field source.

Use local $g$

The value of $g$ depends on location. Use the value stated or the local field strength appropriate to the body’s position; mass does not change when the object is moved.

Common trap

Mass is measured in kilograms and is not a force. Weight is measured in newtons and can change when $g$ changes.

How it is assessed

The evidence asks for the weight of a probe near an asteroid, so select the local value of g rather than automatically using Earth’s surface value.

Command terms

Calculate

What earns marks

Use Fg=mg with the local gravitational field strength and keep mass separate from weight. Check the requested location and report force in newtons.

Watch for

Using the object’s mass as its weight or using Earth’s g when the question gives a different local gravitational field.

Representative question

[Maximum number: 1]

The probe is carried to the asteroid on board a spacecraft.

Calculate the weight of the probe when close to the surface of the asteroid.

A.2.13—Weight

Calculate Weight from Mass

A.2.13 Exam Analysis

Assessment in practice

Question 1