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Circular motion and gravitation
5 MDCAT Physics questions with answers and explanations.
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An object moves at 10 m/s in a circle of radius 5 m. What is its centripetal acceleration?
- 1 2 m/s2
- 2 10 m/s2
- 3 20 m/s2
- 4 50 m/s2
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Correct answer: 20 m/s2
a = v2 / r = 100 / 5 = 20 m/s2, directed toward the centre.
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The escape velocity from a planet depends on:
- 1 The mass of the escaping object
- 2 The mass and radius of the planet
- 3 The colour of the planet
- 4 The speed of the planet's orbit only
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Correct answer: The mass and radius of the planet
Escape velocity = sqrt(2GM / R). It depends on the planet's mass and radius, not on the object that escapes.
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According to Kepler's third law, the square of the orbital period of a planet is proportional to:
- 1 The radius of the orbit
- 2 The cube of the average orbital radius
- 3 The mass of the planet
- 4 The speed of the planet
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Correct answer: The cube of the average orbital radius
T2 is proportional to r3 for planets orbiting the same star.
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The orbital period of a geostationary satellite is:
- 1 90 minutes
- 2 12 hours
- 3 24 hours
- 4 365 days
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Correct answer: 24 hours
It orbits once in 24 hours in the same direction as Earth's spin, so it appears fixed over one point.
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If the distance between two masses is doubled, the gravitational force between them becomes:
- 1 Half
- 2 One quarter
- 3 Double
- 4 Four times
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Correct answer: One quarter
Gravitational force follows an inverse square law, so doubling the distance divides the force by 4.