On a planet similar to earth a vertical hole is drilled from the planet's surface to its centre an object is dropped from the planet's surface and falls toward the planetary centre you may assume that the free-fall acceleration due to gravity varies linearly from 9 9.7ms at the surface to zero at the centre (as it would do if the planet were of uniform density) you may neglect air resistance, and effects due to the planet's rotation the planet's radius is r = 6,420km (a) what is the object's speed when it reaches the planetary centre? number units (b) how long does the object take to reach the planetary centre from the instant it is dropped?