Question

An object is realeased from height of 20 meters. Calculate its kinetic energy just before it hit the ground.

Answer 1

By conservation of energy, we can write:

Total energy of the object at height 20m = total energy of object just before it hits the ground.

__________________

Let the mass of object = m

At height 20m,

velocity = 0
So KE = 1/2 mv^2 = 0

PE = mgh = m×10×20 = 200m

Total energy at height 20 meters = 200m+0 = 200m Joule.
_______________________

Let it's kinetic energy just before it hits ground = KE

Potential energy = mgh = m×10×0 = 0

Total energy = KE + 0 = KE

____________________

Total energy of the object at height 20m = total energy of object just before it hits the ground.

=> 200m = KE

=> KE = 200m Joule

Thus its kinetic energy just before it hit the ground is 200m joule

Answer 2

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By conservation of energy, we can write:

Total energy of the object at height 20m = total energy of object just before it hits the ground.

__________________

Let the mass of object = m

At height 20m,

velocity = 0

So KE = 1/2 mv^2 = 0

PE = mgh = m×10×20 = 200m

Total energy at height 20 meters = 200m+0 = 200m Joule.

_______________________

Let it's kinetic energy just before it hits ground = KE

Potential energy = mgh = m×10×0 = 0

Total energy = KE + 0 = KE

____________________

Total energy of the object at height 20m = total energy of object just before it hits the ground.

=> 200m = KE

=> KE = 200m Joule

Thus its kinetic energy just before it hit the ground is 200m joule.

HOPE SO IT WILL HELP.....