Question

A ball of mass hundred gram is thrown upward it Rises to the maximum height of hundred metre at what height it kinetic energy will be reduced to 60%


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Answer 1

Explanation:

There are two methods by which this can be solved.

With the help of Gravitational PotentialEnergy consideration.With the help of Kinetic energy consideration.

I opt for the GPE method.

a. When the ball is thrown upwards from the ground level, its potential energy is zero and it has maximum kinetic energy.

b. As it rises up, the gravity acting against the direction of motion, its velocity decreasing. Part of its kinetic energy gets converted into its potential energy.

c. As it reaches maximum height, its velocity is momentarily zero. At this point all its kinetic energy has been converted in to its potential energy.

Assuming that no energy is lost against air resistance and applying Law ofconservation of energy we have

Initial Kinetic Energy=Potential Energy at the maximum height

=mgh

=100/1000×9.8×100=98J (Using SI system of units)

Let h1 be the height where kinetic energy is reduced to 60%. From Law of Conservation of energy we know that at this height remaining energy, which is 40%, is potential energy of the ball. Setting up the equation we get

mgh1=mgh×40%

⇒h1=100×40/100=40m