Physics 9702/42 — February/March 2021

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

questions

100

marks

120

minutes

Topics Gravitational Fields · Oscillations · Magnetic Fields · Quantum Physics · Motion in a Circle · Ideal Gases · +8 more

Q1Gravitational FieldsMotion in a CircleFree sample

(a)

State Newton’s law of gravitation.

(b)

Planets have been observed orbiting a star in another solar system. Measurements are made of the orbital radius $r$ and the time period $T$ of each of these planets.

The variation with $R^3$ of $T^2$ is shown in Fig. 1.1.

Fig. 1.1

The relationship between $T$ and $R$ is given by

T^2 = \frac{4\pi^2R^3}{GM}

where $G$ is the gravitational constant and $M$ is the mass of the star.

Determine the mass $M$ .

$M$ = ______ $\text{kg}$

(c)

A rock of mass $m$ is also in orbit around the star in (b). The radius of the orbit is $r$ .

(i)

Explain why the gravitational potential energy of the rock is negative.

(ii)

Show that the kinetic energy $E_k$ of the rock is given by

E_k = \frac{GMm}{2r}

(iii)

Use the expression in (c)(ii) to derive an expression for the total energy of the rock.

The rest of this paper

11 more questions

Q2Ideal Gases6M
Q3Temperature8M
Q4Oscillations9M
Q5Communication7M
Q6Gravitational Fields · Electric Fields · Capacitance7M
Q7Electronics9M
Q8Magnetic Fields · Quantum Physics8M
Q9Magnetic Fields · Oscillations10M
Q10Alternating Currents8M
Q11Medical Physics · Quantum Physics10M
Q12Nuclear Physics6M

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