The gravitational force between two point masses is proportional to the product of the masses and inversely proportional to the square their separation
The gravitational force between two masses outside a uniform field is defined by Newton’s Law of Gravitation
A satellite with a mass of 6500 kg is orbiting the Earth at 2000 km above the Earth's surface. The gravitational force between them is 37 kN.
Calculate the mass of the Earth.
Radius of the Earth = 6400 km.
The electrostatic force between two point charges is proportional to the product of the charges and inversely proportional to the square of their separation
The electrostatic force between two charges is defined by Coulomb’s Law
An alpha particle is situated 2.0 mm away from a gold nucleus in a vacuum. Assuming them to be point charges, calculate the magnitude of the electrostatic force acting on each of the charges. Atomic number of helium = 2, Atomic number of gold = 79, Charge of an electron = −1.60 × 10-19 C.
Step 1: Write down the known quantities
Step 2: The electrostatic force between two point charges is given by Coulomb’s LawExam Tip
A common mistake in exams is to forget to add together the radius of the planet (which is the distance from the centre of mass to the surface) and then, the height above the surface of the planet.
Sketching a diagram will remind you of these two distances and is really a few seconds well spent!