Relative to the floor it's resting on, its height is zero,
so its potential energy is zero.
Relative to the next floor down, its height could be
three or four meters, and it could have plenty of
potential energy ... if you cut out a circle in the floor
all around the rock, and let it fall to next floor down,
it could really do some damage. Look out below ! !

You just do the calculations.
Answer:
19.62 ms
Explanation:
t = Time taken = 2 s
u = Initial velocity
v = Final velocity
s = Displacement
a = Acceleration due to gravity = 9.81 m/s² (downward direction is taken as positive)
Equation of motion

The speed of the pebble when it hit the water is 19.62 ms
Answer:

Explanation:
Given
Density = 3 starts in 10 cubic light years.
Required
Determine the probability of 1 or more in 10 cubic light years
Since the number of stars follow a Poisson distribution, we make use of:




T = the light years

Calculating 
In probability:

Calculating P(X=0)
Substitute 0 for k and the values for
and T in








Substitute 0.04979 for P(X=0) in 


--- approximated
<em>Hence, the required probability is 0.9502</em>
Answer:
Density, mass of a unit volume of a material substance. The formula for density is d = M/V, where d is density, M is mass, and V is volume. Density is commonly expressed in units of grams per cubic centimetre. ... Density can also be expressed as kilograms per cubic metre (in metre-kilogram-second or SI units).
The density of water is about 1 g/cm3, since the gram was originally defined as the mass of one cubic centimetre of water at its maximum density at 4 °C.