Question

Q no7:- When a stone falls through a vertical height 'h' the decrese in the gravitatonal
P.ES:
a. mg/h
b. mg/h
C. mgh
d. mg
​

Answer 1

Given:

Stone of mass m , falls down a height h .

To find:

Decrease in Gravitational Potential Energy

Concept:

Gravitational Potential Energy is actually an scalar index representing the strength of gravitation field in a particular region.

Calculation:

Let reference line be located at lower point .

So initial potential energy at height h be PE1

PE1 = m × g × h = mgh

Potential at lower point be PE2

PE2 = m × g × 0 = 0

So decrease in Potential Energy will be :

∆PE = PE2 - PE1

=> ∆PE = 0 - mgh

=> ∆PE = - mgh

So final answer :

$\boxed{ \red{ \bold{ \huge{\Delta PE = -mgh}}}}$

We can also say that decrease in Potential Energy is mgh.

Answer 2

$\bold{\bf{\blue{Change\;in\;Potential\;Energy\;,\;\Delta P=P_2-P_1}}}$

$\bold{Potential\;Energy\;,\;P=mgh}$

where ,

• m denotes mass
• g denotes gravitational force
• h denotes height

When stone is at height h , the potential energy will be ,

$\bold{P_1=mgh}$

When stone reaches the ground , the potential energy will be ,

[ height is zero ]

$\bold{P_2=mg(0)}\\\\\implies \bold{P_2=0}$

Now , change in potential energy ,

$\bold{\Delta P=P_2-P_1}\\\\\implies \bold{\Delta P=0-mgh}\\\\\implies \bold{\bf{\blue{\Delta P=-mgh}}}$

So , decrease in potential energy is mgh

So  Option C is correct .

More Information :

Potential Energy :

• Potential energy is the energy a system has due to position, shape, or configuration. It is stored energy that is completely recoverable. A conservative force is one for which work done by or against it depends only on the starting and ending points of a motion and not on the path taken.