The four planets that orbit closest to the sun are best described as

Terrestrial planets

Explanation:

The first four planets which are closest to the sun are called as terrestrial planets. These terrestrial planets include Mercury, Venus, Earth and Mars. These planets are called terrestrial because they are earth like and are made up of either terrestrial substance such as rock, soil etc. or metals such as iron, manganese, etc. They also possess terrestrial features such as valleys, volcanoes and craters.

a) time taken = 1.427 s

b) final speed before hitting the ground = 14 m/s

Explanation:

height of cliff = 10 m

acceleration due to gravity = 9.81

time taken for stone to reach bottom of cliff = ?

velocity of stone just before hitting the ground = ?

To find the time taken, we will use Newton's equation of motion

using

where

v = final speed of stone before hitting the ground

u = initial speed of the stone (u = 0 since the stone started falling from rest)

a = acceleration due to gravity = 9.81

s = height of the cliff = 10 m

Solving, we have

From the first equation of motion,

where t = time taken for stone to reach bottom of cliff

imputing values, we have