Exercise n ° 3: Use a formula (4 pts)
1) An object of mass m = 500 g is suspended from a dynamometer on Mars and it indicates 1.8 N.
Calculates the value of the intensity of gravity on Mars. (2 pts)
2) Calculate the mass of an object whose weight on Neptune is 2.75 N knowing that the intensity of gravity on
Neptune is g = 11 N / kg.
Answers
Answer:
All objects with mass have a gravitational field around them. A gravitational field is where a mass experiences a force.
All matter has a gravitational field that attracts other objects. The more mass an object has, the greater its gravitational field will be. For example, the Earth has a greater gravitational field than the Moon because it has a much greater mass than the Moon. The Moon is attracted to the Earth because it is within the Earth’s gravitational field.
Gravitational fields
The formula that links mass and gravitational field strength is:
gravity force = mass × gravitational field strength (g)
This is when:
gravity force is measured in newtons (N)
mass is measured in kilograms (kg)
gravitational field strength (g) is measured in newtons per kilogram (N/kg)
The Earth’s gravitational field strength (g) is 10 N/kg. This means that for each kg of mass, an object will experience 10 N of force.
What is weight?
Weight refers to the gravity force of planets and other bodies in the Universe, and the effect that this has on objects. It is important to remember that weight is not the same as mass - the weight of an object and its mass are directly proportional. This means that for a given gravitational field strength, the greater the mass of the object, the greater its weight.
Weight is a non-contact force because gravity exerts its force through a field. An object does not need to be touching the Earth to have a weight. The weight of an object can be measured using a calibrated spring-balance, often called a Newton meter. Weight is also referred to as ‘gravity force’.
gravity force = mass × gravitational field strength (g)
This is when:
gravity force (weight) is measured in newtons (N)
mass is measured in kilograms (kg)
gravitational field strength (g) is measured in newtons per kilogram (N/kg)
The equation can be rearranged to make mass the subject:

Example
Calculate the gravity force (weight) of a skydiver with a mass 70 kg falling towards the Earth?
(Remember that gravitational field strength = 10 N/kg on Earth).
weight = mass × gravitational field strength
weight = 70 × 10
weight = 700 N