# A-level Physics (Advancing Physics)/Large Units/Worked Solutions

**1. What is one parsec in m?**

206265 AU x 150 x 10^{9} = 3.09 x 10^{16}m

**2. Convert 3 light days into km.**

c = 3 x 10^{5}kms^{−1}

3 x 3 x 10^{5} x 24 x 60 x 60 = 7.78 x 10^{10}km

**3. Convert 5.5 parsecs into light years.**

1 ly = 9.46 x 10^{15}m

5.5 pc = 5.5 x 3.09 x 10^{16}m = 1.70 x 10^{17}m

Divide by 1 ly in metres to get a final answer of approximately 18ly.

**4. The difference in angle of a star on the perpendicular to the plane of the Earth's orbit which passes through the Sun when viewed from either side of the Earth's orbit is 0.1°. How far away is the star in parsecs?**

The angle between the perpendicular and the line which goes through the Earth is 0.05° = 180". So, the star is 1/180 pc away.