Question

A coconut of mass 1kg falls to the earth from a height of 10m. The Kinetic energy of the coconut when it is 4m above the ground is_______.
(A)0.588J
(B)58.8J
(C)5.88J
(D)588J​

Answer 1

answer : option (B) 58.8J

explanation : mass of coconut , m = 1kg

initial velocity of coconut , u = 0

initial height of coconut , hi = 10m

final height of coconut , hf = 4m

according to conservation of energy ,

change in kinetic energy + change in potential energy

or, change in kinetic energy = - change in potential energy

or, (final kinetic energy - initial kinetic energy) = -(final potential energy - initial potential energy)

or, (final kinetic energy - 1/2 m(0)² ) = -(mg.hf - mg.hi)

or, final kinetic energy = -mg(hf - hi)

= -1kg × 9.8 m/s² (4m - 10m)

= 9.8 × 6 J

= 58.8 J

hence, kinetic energy of the coconut when it is 4m above the ground is 58.8J