Show that the total mechanical energy of a freely falling body under gravity is conserved.
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Answer:
The mechanical energy of a freely falling body under gravity is constant.
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Yes
when body is at height h
it's doesn't have any kinetic energy but it has potential energy which is equal to 'mgh' where m is mass of body ,g is acceleration due to gravity
and h is the height above the ground where body is situated
so mechanical energy at that point will be mgh
case 2 when body is at height h/2
for this kinetic energy is equal to 1/2 *m*(v)²
but v² - u²= 2as
since u is 0
so v² =2as
but a=g and s= h/2
so v² = 2* g* h/2= 2gh
so kinetic energy will be mgh/2
and potential energy is mgh/2
so mechanical energy is mgh
case 3 when body touches the ground
kinetic energy is 1/2m v²
but v²-u²=2as
but a =g and s=h and u= 0
so v²=2gh
so kinetic energy = mgh
but at ground potential energy is 0
so mechanical energy is mgh
from case 1 ,case2 and case 3
mechanical energy is conserved
(important note the h in kinetic energy is the height covered by body but in potential energy is the height at which body is situated)