Physics 9702/42 — May/June 2012

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

questions

100

marks

120

minutes

Topics Gravitational Fields · Electric Fields · Communication · Motion in a Circle · Oscillations · Thermodynamics · +8 more

Q1Gravitational FieldsMotion in a CircleFree sample

(a)

State Newton’s law of gravitation.

(b)

The Earth and the Moon may be considered to be isolated in space with their masses concentrated at their centres.

The orbit of the Moon around the Earth is circular with a radius of $3.84 \times 10^5\ \text{km}$ . The period of the orbit is $27.3$ days.

Show that

(i)

the angular speed of the Moon in its orbit around the Earth is $2.66 \times 10^{-6}\ \text{rad s}^{-1}$ ,

(ii)

the mass of the Earth is $6.0 \times 10^{24}\ \text{kg}$ .

(c)

The mass of the Moon is $7.4 \times 10^{22}\ \text{kg}$ .

(i)

Using data from (b), determine the gravitational force between the Earth and the Moon.

force = ______ $\text{N}$

(ii)

Tidal action on the Earth’s surface causes the radius of the orbit of the Moon to increase by $4.0\ \text{cm}$ each year.

Use your answer in (i) to determine the change, in one year, of the gravitational potential energy of the Moon. Explain your working.

energy change = ______ $\text{J}$

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