Question

A body of mass 20kg is kept at a height 20m from the ground , when it is released after sometime it's kinetic energy becomes 450J. What will be the potential energy of the body at the instant ?​

Answer 1

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we know potential energy mgh at 20m above ground will be mgh = 20×10×20 = 4000j

the moment he strike the ground , then it's height will be 0 so , whole Potential will change to kinetic energy

So kinetic energy = 4000j

Answer 2

when the object is at height 20m

potential energy = mgh = 20×10×20 = 4000

kinetic energy at 20m = 1/2mv² = 0

from conservation of energy

P.E + K.E = constant ........(i)

when kinetic energy = 450J

let potential energy at this point be x

so, from (i)

x J + 450 J = 4000 J + 0J

x = 4000 J - 450 J

x = 3550 J

so, P.E at this point = 3550 J