Gravitation: Practice Questions (Form 4 SPM Physics)

F = G m₁m₂ / r² = (6.67 × 10⁻¹¹ × 5 × 10) / 2² = 8.34 × 10⁻¹⁰ N.

g = GM / r² = (6.67 × 10⁻¹¹ × 6.0 × 10²⁴) / (6.4 × 10⁶)² = 9.77 m s⁻².

T₂² / r₂³ = T₁² / r₁³ → T₂² = T₁² (r₂/r₁)³ = 1² × 4³ = 64, so T₂ = 8 yr.

v = √(GM / r) = √((6.67 × 10⁻¹¹ × 6.0 × 10²⁴) / 7.0 × 10⁶) = 7.56 × 10³ m s⁻¹.

Astronauts float not because gravity is gone, but because they and their spacecraft are falling around the Earth together, so nothing pushes up on them.

A satellite stays in orbit because gravity constantly pulls it toward Earth while it moves sideways fast enough to keep curving around instead of falling in.

Gravitational field strength is the gravitational force acting on each kilogram of mass. On Earth's surface it is about 9.81 N per kg, which is also the free-fall acceleration.

An orbit above the equator in which a satellite has a period of 24 hours, so it appears to stay above the same point on the Earth's surface.

The minimum velocity an object needs to completely escape the gravitational pull of a planet or other body.

The velocity a satellite must have to stay in a stable orbit at a given radius, where gravitational force provides the centripetal force.

The universal constant G in Newton's law of gravitation, with a value of about 6.67 × 10⁻¹¹ N m² kg⁻².

The net force directed towards the centre of a circle that keeps an object moving in a circular path, such as a satellite in orbit.

Every mass attracts every other mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres.