10km/10min is a legitimate speed. So is meters/sec, km/hour (kph), etc.
Kph is very common for vehicles:
10 km/10 min (60 min/hr) = 60 kph
I would rather be hit by the deflated ball because it wouldn't hurt as bad because it wouldn't have a lot of weight to hurt me in anyway
The complete statement is
As a solid element melts, the atoms become more separated and they have less attraction for one another.
Let me explain to you how this happens. In solid phase. Its molecules are arranged in a very compact manner that is why it takes a definite shape and volume. When it is heated, the kinetic energy of the molecules increases. This is characterized by more frequent collisions. The rise in temperature causes the molecules to move rapidly by vibrating. When it reaches an amount of energy that causes the solid to change phase, this is called the latent energy. The molecules break their form and move farther away from each other until it resembles that of a liquid melting. At this point, the molecules would have lesser attraction because of the distance between them.
Consider the upward direction of motion as positive and downward direction of motion as negative.
a = acceleration due to gravity in downward direction = - 9.8 
v₀ = initial velocity of rock in upward direction = ?
v = final velocity of rock at the highest point = 0 
t = time to reach the maximum height = 4.2 sec
Using the kinematics equation
v = v₀ + a t
inserting the values
0 = v₀ + (- 9.8) (4.2)
v₀ = 41.2
