(a)[2]
No external forces are acting on the object. Describe two features of the object’s motion that follow from Newton’s first law.
(b(i))[1]
Venus experiences an external force as it orbits the Sun. State why a force must act on Venus to keep it following an approximately circular orbit.
(b(ii))[3]
State what produces this force, and state the direction in which the force acts.
(b(iii))[2]
The average radius of Venus’s orbit is $1.1\times10^{11}\,\text{m}$. Venus takes 5400 hours to complete one orbit of the Sun. Calculate the average orbital speed of Venus around the Sun.
(b(iv))[2]
Planet X is closer to the Sun than Venus. State the name of planet X and state how its orbital speed around the Sun compares with the orbital speed of Venus.