Paper 1 Gravitational Fields Answers

Q	Ans	Brief reason
1	B	Newton’s law is inverse-square.
2	C	$F\propto 1/r^2$.
3	A	$\vec{g}=\vec{F}/m$.
4	A	Equivalent to $\mathrm{m}{\mathrm{s}}^{-2}$.
5	B	Gravity is attractive.
6	B	Potential is the work done per unit mass in bringing a small test mass from infinity to the point; equivalently, it is potential energy per unit mass.
7	B	Work is released approaching from infinity, so $\varphi <0$.
8	B	$\varphi =-GM/r$.
9	B	Potential has no direction.
10	A	Equal opposite field vectors cancel.
11	B	Potentials are scalars and add, both negative.
12	C	Gravity is the inward resultant.
13	A	From $GMm/r^2=m{v}^2/r$.
14	B	$v=\sqrt{GM/r}$.
15	C	It matches Earth’s rotation period.
16	A	It must remain above the same point on Earth.
17	B	$g=GM/r^2$.
18	A	$\vec{g}$ is related to the negative potential gradient.
19	B	Gravitational interaction between masses is attractive.
20	A	$U=m\varphi$.