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| Potential Energy |
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 Water stored in a reservoir is capable of rotating turbines kept at a lower level. Water stored in a reservoir possesses energy by virtue of its position. |
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 A nail hit hard with a hammer gets fixed while if the hammer is just placed on the nail, the nail hardly moves. The hammer, which is raised, possesses energy by virtue of its position. |
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 A toy car driven by a winding key: When we turn the key the spring gets wound. When we let go, the wheels of the toy car start turning due to the unwinding of the spring, and the car moves if left on the floor. Wound spring possesses energy. The gain in energy is due to the position or condition of the spring. |
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| A Toy Car Driven by a Winding Key |
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| Stretched String Gains Potential Energy |
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| Potential energy of an object can be defined as the energy possessed by the object by virtue of its position or condition. |
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| Consider an object of mass 'm', raised through a height 'h' above the earth's surface. The work done against gravity gets stored in the object as its potential energy (gravitational potential energy). |
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| Therefore, potential energy = work done in raising the object through a height 'h'. |
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| Object of Mass 'm', Raised Through a Height 'h' |
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| Potential energy = F x S …(1) |
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| But F = mg [Newton's second law of motion] |
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| S = h |
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| Substituting for F and S in equation (1), we get |
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| Potential energy = mg x h |
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 Potential energy = mgh |
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| From the above relation it is clear that the potential energy of an object depends on the height from the ground. |
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| 01. A body of mass 2 kg is raised to a height of 25 m. Calculate the potential energy possessed by the body. |
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| Solution: |
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| Mass of the body (m) = 2 kg |
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| Height (h) = 25 m |
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| Potential energy of the body = mgh |
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| 02. A bag of rice weighs 75 kg. To what height is it raised if the work done in lifting it is 4900 J. |
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| Solution: |
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| Mass of the bag of rice = 75 kg |
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| Work done = 4900 J |
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| Work done in lifting the bag of rice is stored in it as its potential energy. |
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| Therefore, Potential energy = mgh |
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| Height = 6.67 m |
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