Question

How potential energy of a particle changes into kinetic energy?

Answer 1

Its not equal to zero.

The principle of the conservation of mechanical energy states that the total mechanical energy in a system (i.e., the sumof the potential plus kinetic energies) remains constant) as long as the only forces acting are conservative forces.

A good way to think of conservative forces is to consider gravity; you throw a ball straight up, and it leaves your hand with a certain amount of kinetic energy. At the top of its path, it has no kinetic energy, but it has a potential energy equal to the kinetic energy it had when it left your hand. When you catch it again it will have the same kinetic energy as it had when it left your hand. All along the path, the sum of the kinetic and potential energy is a constant, and the kinetic energy at the end, when the ball is back at its starting point, is the same as the kinetic energy at the start, so gravity is a conservative force.

Kinetic friction, on the other hand, is a non-conservative force, because it acts to reduce the mechanical energy in a system. Note that non-conservative forces do not always reduce the mechanical energy; a non-conservative force changes the mechanical energy, so a force that increases the total mechanical energy, like the force provided by a motor or engine, is also a non-conservative force.

Hope your query is satisfied.

THANKS FOR READING.

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Kartik Dolas, Student

Answered Jul 26, 2017

Kinetic energy of a moving object is given by KE =½mv² and potential energy of an object is given by PE =mgh.

Here h- height from ground level

V- velocity of moving object

Total energy is sum of kinetic energy and potential energy.

T.E. = K.E. +P.E.

T.E.= ½mv²+mgh

So it can be zero if

Case I ) m=0

For any object whose mass is zero… sum of PE and me is zero.

But till present we haven't discovered an object which exists but still it mass is zero… weight can be zero but mass cannot be zero.(exception :- light particle I.e. photon have zero mass.. but we cannot apply Newtonian mechanics on it)

Hence this case is eliminated.. as m cannot be zero

Case II ) If h and v are simultaneously zero

If an object rests on ground (h=0) and it is not moving (v=0).. then sum of PE and KE will be zero.

T.E.= ½m(0)² +mg(0)= 0……….(1)

But if the object is lifted by height h1 it's PE will change and will become = mgh1.. as the velocity of object is 0.. KE will be zero.

Now new T.E. will become

T.E.¹ = ½m(0)² +mg(h1) = mgh1……..(2)

But Total energy for equation 1 and 2 are different

According to law of conservation of energy,”total energy of an object remains constant.”

So this case is also eliminated.

Resultantly.. there exists no case when PE and KE are simultaneously zero or total energy I.e. (PE+KE) is zero.

Ans :- sum of potential and kinetic energy for an object will never be zero.

Solution is little bit boring and maths oriented.. but I assure that it will clear your concept for long run.

Thanks!!