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IB Physics: Gravitational fields — Practice Questions & Answers
236 practice questions available for this topic — here are 10 with full answers and explanations.
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Practice questions with answers
1
Multiple choice · Medium
Newton's law of gravitation gives the force between two point masses as:
- $F=\frac{Gm_{1}m_{2}}{r^{2}}$
- $F=\frac{Gm_{1}m_{2}}{r}$
- $F=Gm_{1}m_{2}r^{2}$
- $F=\frac{G(m_{1}+m_{2})}{r^{2}}$
Tap an answer to check it.
Why$F=\frac{Gm_{1}m_{2}}{r^{2}}$, an inverse-square attraction proportional to the product of the masses.
2
Multiple choice · Easy
The gravitational field strength at a point is defined as the force per unit:
Tap an answer to check it.
Why$g=\frac{F}{m}$, the gravitational force per unit mass, measured in $\text{N kg}^{-1}$.
3
Multiple choice · Easy
A $3.0\,\text{kg}$ mass is in a field where $g=9.8\,\text{N kg}^{-1}$. What is its weight?
- $29\,\text{N}$
- $3.0\,\text{N}$
- $9.8\,\text{N}$
- $0.31\,\text{N}$
Tap an answer to check it.
Why$W=mg=3.0\times 9.8=29.4\,\text{N}$.
4
Multiple choice · Medium
The gravitational field strength at the surface of a planet of mass $M$ and radius $r$ is:
- $g=\frac{GM}{r^{2}}$
- $g=\frac{GM}{r}$
- $g=GMr^{2}$
- $g=\frac{Gr^{2}}{M}$
Tap an answer to check it.
Why$g=\frac{GM}{r^{2}}$, obtained by dividing the gravitational force by the test mass.
5
Multiple choice · Hard
If the distance between two masses is doubled, the gravitational force between them becomes:
- One quarter of the original
- Half of the original
- Double the original
- Four times the original
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WhyGravity follows an inverse-square law, so doubling $r$ gives a force of $\frac{1}{2^{2}}=\frac{1}{4}$ of the original.
6
Multiple choice · Medium
For a satellite in a stable circular orbit, the gravitational force provides the:
- Centripetal force
- Tangential thrust
- Normal reaction
- Frictional force
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WhyGravity supplies the centripetal force needed to keep the satellite moving in its circular orbit.
7
Fill in the blank · Easy
Gravitational field strength is the gravitational force exerted per unit .
Answer:
mass
Why$g=\frac{F}{m}$, with units of $\text{N kg}^{-1}$, numerically equal to free-fall acceleration.
8
Fill in the blank · Medium
Because gravity obeys an inverse-square law, tripling the separation reduces the force to of its original value.
Answer:
1/9 / one ninth / a ninth
Why$F\propto\frac{1}{r^{2}}$, so at $3r$ the force is $\frac{1}{3^{2}}=\frac{1}{9}$ of the original.
9
Multiple choice · Medium
The gravitational field strength at the surface of a spherical planet of mass M and radius r is
- G M / r squared
- G M / r
- G M r squared
- G M squared / r
Tap an answer to check it.
WhySurface field strength g = G M / r squared.
10
Multiple choice · Medium
Two planets have equal mass, but planet B has twice the radius of planet A. The surface gravitational field strength of planet B is
- one quarter that of planet A
- half that of planet A
- twice that of planet A
- the same as planet A
Tap an answer to check it.
Whyg is proportional to 1/r squared, so doubling r gives one quarter the field strength.
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