Circular motion and gravitation

Written by Dr. Hamza Farooq (Physics)

MDCAT · Physics · 5 questions

Name: ____________________ Date: ____________

An object moves at 10 m/s in a circle of radius 5 m. What is its centripetal acceleration?
- A 20 m/s²
- B 10 m/s²
- C 2 m/s²
- D 50 m/s²
The escape velocity from a planet depends on:
- A The speed of the planet's orbit only
- B The colour of the planet
- C The mass and radius of the planet
- D The mass of the escaping object
According to Kepler's third law, the square of the orbital period of a planet is proportional to:
- A The cube of the average orbital radius
- B The speed of the planet
- C The mass of the planet
- D The radius of the orbit
The orbital period of a geostationary satellite is:
- A 12 hours
- B 90 minutes
- C 365 days
- D 24 hours
If the distance between two masses is doubled, the gravitational force between them becomes:
- A Four times
- B Double
- C Half
- D One quarter

Answer key

1. A, 2. C, 3. A, 4. D, 5. D

a = v² / r = 100 / 5 = 20 m/s², directed toward the centre.
Escape velocity = sqrt(2GM / R). It depends on the planet's mass and radius, not on the object that escapes.
T² is proportional to r³ for planets orbiting the same star.
It orbits once in 24 hours in the same direction as Earth's spin, so it appears fixed over one point.
Gravitational force follows an inverse square law, so doubling the distance divides the force by 4.