Physics 9702 · AS & A Level · Gravitational field of a point mass
Gravitational field of a point mass — practice question
Fig. 3.1 displays a single isolated point mass with mass $M$. Point P is located a distance $x$ from this mass. In Fig. 3.3, two identical isolated uniform spheres X and Y, each with radius $R$, have centres separated by a distance $L$ as shown. Point P lies on the line joining the centres of X and Y, and its variable displacement from the centre of sphere X is $x$. The gravitational field strength at the surface of each sphere is $g_0$.
(a)[1]
Define the gravitational field at a point.
(b(i))[2]
By considering the force exerted by the point mass on a test mass of mass $m$ placed at P, derive an equation for the gravitational field strength $g$ at P, in terms of $M$ and $x$. Identify any other symbols you use.
(b(ii))[1]
On Fig. 3.1, draw an arrow showing the direction of the gravitational field at P.
(b(iii))[2]
Fig. 3.2 shows point Q at a distance $\frac{x}{2}$ from the point mass, on the opposite side of the mass from P. Compare the gravitational field at Q with that at P.
(c)[3]
On Fig. 3.4, sketch the variation of the gravitational field $g$ at point P with $x$ for $x = R$ to $x = L - R$.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “force per unit mass on a test mass” …