Question

A 20 kilogram rock is dropped off the top of a 30 meter tall building. what is the kinetic energy of the rock right before it impacts the ground

Answer 1

The answer would be 12.5

Answer 2

Answer : The kinetic energy of the rock is, 5880 J

Explanation :

Potential energy is defined as the energy possessed due to the height of the object.

Mathematically,

`E_p=mgh`

where,

`E_p` = potential energy of the rock at height of 30 m= ?

m = mass of rock = 20 kg

g = acceleration due to gravity =
`9.8m/s^2`

h = height of the bridge from where the rock = 30 m

Putting values in above equation, we get:

`E_p=(20kg)* (9.8m/s^2)* (30m)\\\\E_p=5880J`

According to the law of conservation of mass,

Potential energy = Kinetic energy = 5880 J

Thus, the kinetic energy of the rock is, 5880 J