(a) What is the difference between gravitational potential energy and elastic potential energy? Give one example of a body having gravitational potential energy and another having elastic potential energy.
(b) If $784\ J$ of work was done in lifting a $20\ kg$ mass, calculate the height through which it was lifted.


(a). Difference between gravitational potential energy and elastic potential energy:


Gravitational Potential EnergyElastic Potential Energy
1. If a body is placed at a certain height from the ground then potential energy due to height is said to be gravitational potential energy of the body.1. Energy gained by a body by changing its shape and size is known as the elastic potential energy of the body. 
2. Gravitational potential energy of a body is due to gravitational force.2. Elastic potential energy is due to the elastic property of the body.
3. A stone placed on the roof is an example of a body possessing gravitational potential energy.3. An stretched spring is a good example of the body possessing elastic potential energy.



(b). Work done $W=784\ J$


Mass $m=20\ kg$


Let $h$ be the height.


On placing these values into $W=mgh$


$784=20\ kg.\times9.8\ m/s^2\times h$    [take $g=9.8\ m/s^2$]


Or $h=\frac{784}{20\times9.8}$


Or $h=4\ m$


Therefore, the mass was lifted to a height of $4\ m$.

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Updated on: 10-Oct-2022

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