Fig. 1 shows a long-period comet on an elliptical path through the Solar System. The arrow near the comet shows the direction of its motion. The tail is dra...
Question 1 Report
Fig. 1 shows a long-period comet on an elliptical path through the Solar System. The arrow near the comet shows the direction of its motion. The tail is drawn pointing away from the Sun because particles and gas are pushed outward by solar radiation and the solar wind. At its closest point, the comet passes inside the orbit of Mars. Its orbit takes several thousand years, so it is seen from the Earth only rarely.
(a) State the name of the path followed by the comet. [1]
(b) State whether the tail points towards or away from the Sun. [1]
(c) Explain why the tail does not always trail behind the comet's direction of motion. [2]
(d) Describe how the speed of the comet changes as it travels from the farthest part of its orbit towards the Sun. [2]
(e) Explain why the gravitational force on the comet changes during its orbit. [2]
(f) Calculate the time in seconds for an orbit period of 3200 years. Use 365 days per year. [3]
(g) Calculate the mean orbital speed if the comet travels 1.20 × 1013 km in this time. [2]
(h) State why a comet can return after thousands of years instead of escaping permanently from the Solar System. [1]
Answer Details
(a) The comet follows an elliptical orbit, or ellipse. [1]
(b) Its tail points away from the Sun. [1]
(c) The tail direction is set by radiation pressure and the solar wind from the Sun. This is independent of the comet's direction of motion, so the tail does not necessarily trail behind it. [2]
(d) The comet's speed increases as it moves towards the Sun, and it is fastest near the Sun. [2]
(e) The separation between the comet and Sun changes during the elliptical orbit. A smaller separation gives a stronger gravitational force. [2]
(f) \[t=3200\times365\times24\times3600=1.01\times10^{11}\text{ s}\]
[3]
(g) \[v=\frac{1.20\times10^{13}\text{ km}}{1.01\times10^{11}\text{ s}}=119\text{ km/s}\approx1.2\times10^2\text{ km/s}\]
[2]
(h) The Sun gravitationally attracts the comet and keeps it in a bound orbit, allowing it to return. [1]
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