(a) By reference to the definition of gravitational potential, explain why gravitational potential is a negative quantity. (b) Two stars A and B have their surfaces separated by a distance of $1.4 \times 10^{12}\ \text{m}$, as illustrated in Fig. 1.1. Point P lies on the line joining the centres of the two stars. The distance $x$ of point P from the surface of star A may be varied. The variation with distance $x$ of the gravitational potential $\phi$ at point P is shown in…

Physics 9702/41 — May/June 2016

Cambridge A-Level · A Level Structured Questions · worked solutions for every part, with the mark scheme

questions

100

marks

120

minutes

Topics Magnetic Fields · Quantum Physics · Gravitational Fields · Ideal Gases · Oscillations · Medical Physics · +6 more

Q1Gravitational FieldsFree sample

(a)

By reference to the definition of gravitational potential, explain why gravitational potential is a negative quantity.

(b)

Two stars A and B have their surfaces separated by a distance of $1.4 \times 10^{12}\ \text{m}$ , as illustrated in Fig. 1.1.

Fig. 1.1

Point P lies on the line joining the centres of the two stars. The distance $x$ of point P from the surface of star A may be varied.

The variation with distance $x$ of the gravitational potential $\phi$ at point P is shown in Fig. 1.2.

Fig. 1.2

A rock of mass $180\ \text{kg}$ moves along the line joining the centres of the two stars, from star A towards star B.

(i)

Use data from Fig. 1.2 to calculate the change in kinetic energy of the rock when it moves from the point where $x = 0.1 \times 10^{12}\ \text{m}$ to the point where $x = 1.2 \times 10^{12}\ \text{m}$ .
State whether this change is an increase or a decrease.

change = ______ $\text{J}$

(ii)

At a point where $x = 0.1 \times 10^{12}\ \text{m}$ , the speed of the rock is $v$ .

Determine the minimum speed $v$ such that the rock reaches the point where $x = 1.2 \times 10^{12}\ \text{m}$ .

minimum speed = ______ $\text{m s}^{-1}$

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